Anyone who has spent a weekend flashing SD cards for a $60 Anbernic handheld knows the frustration: half the setup guides on YouTube reference software that stopped shipping updates a year ago. That confusion is the whole story of custom firmware for budget retro handhelds in August 2026. Three names dominate the search results — muOS, ArkOS, and JELOS — but only one of them is still receiving active development. The other two are effectively frozen, and understanding why matters more than any feature checklist.
This comparison breaks down what each project actually is today, which devices they support, what replaced the ones that died, and which one you should flash onto your RG35XX, R36S, or RGB30 this month. The short version: muOS is the actively maintained option for Anbernic’s RG35XX/RG40XX family and TrimUI handhelds, ArkOS’s original maintainer walked away in mid-2025, and JELOS was archived back in May 2024 and reborn under a new name, Rocknix. None of that is obvious from a Google search, which is exactly why this guide exists.
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What muOS, ArkOS, and JELOS Actually Are
All three projects solve the same basic problem. Budget retro handhelds — the $50-$90 class of devices from Anbernic, Powkiddy, and their many clones — ship with stock firmware that is usually clunky, ad-laden, or missing basic quality-of-life features like Wi-Fi sync, proper save states, or a usable theme engine. Custom firmware (CFW) replaces that stock software entirely, usually flashed onto a second SD card so the original firmware stays untouched as a fallback.
muOS (also called MustardOS) is a from-scratch custom firmware focused tightly on Anbernic’s RG35XX family — the original RG35XX, RG35XX Plus, RG35XX H, the 2024 refresh, RG35XX SP, RG35XX Pro, plus the RG28XX, RG34XX, RG40XX H/V, and RGCubeXX — along with TrimUI Brick and TrimUI Smart Pro. Handhelds.wiki’s device page, last updated in May 2026, counts 11+ officially supported Anbernic and TrimUI models running the current MustardOS 2601.1 build. It is built around a clean, console-like menu system rather than the EmulationStation front end most rivals use, ships PortMaster preinstalled through a muos.portmaster.zip package PortMaster’s own site last refreshed in March 2026, and it ships its own theming and overlay system tuned per device.
ArkOS is an Ubuntu-based OS built specifically for Rockchip (RK3326/RK3566) handhelds — think Anbernic’s RG351 and RG353 lines, the RG503, and a long list of Powkiddy devices (RGB10, RGB20, RGB30, RK2020, RK2023) plus RK3326 clones like the R36S and R35S. It uses the EmulationStation front end and bundles PortMaster for native ports of games like Doom and Quake, a workflow RetroGameCorps documented in detail back when the project was under active development.
JELOS (Just Enough Linux OS) took a different technical approach: an immutable Linux distribution, meaning the base OS partition is read-only and updates apply as atomic swaps rather than in-place file changes. It targeted much the same RK3566 hardware as ArkOS — RG353P/M/V/VS, RG503, Powkiddy RK2023, RGB30, RGB10 Max 3, and the Powkiddy X55 — plus a handful of single-board computer builds like the Orange Pi 5.
It’s worth understanding why this fragmented landscape exists in the first place. Budget handheld makers rarely write good software themselves — their margins are built around cheap Rockchip and Allwinner SoCs, and the firmware that ships in the box is often a barely modified Android or Linux build with a shell of a launcher on top. That gap is what volunteer developers stepped in to fill, one SoC family at a time. Because each project started by targeting whatever hardware its own creator happened to own, the ecosystem never consolidated into a single universal CFW the way, say, Android did for phones. Instead you get a patchwork: muOS for Anbernic’s newer Allwinner chips, ArkOS (and its descendants) for the older Rockchip RK3326 wave, and JELOS/Rocknix for the RK3566 generation that followed. Knowing which SoC family your specific handheld uses is often more useful than knowing which firmware has the flashiest feature list.
It also explains why “which firmware is best” is the wrong question for most buyers. The right question is “which firmware is actively maintained for the exact device I own or am about to buy,” because in this segment of the market, feature parity between projects is common but maintenance status is not. A firmware with slightly fewer bells and whistles but a maintainer who ships monthly bug fixes will beat a feature-rich project that stopped responding to GitHub issues a year ago, every time, once you actually try to use it for more than a weekend.
The Uncomfortable Truth: Two of Three Are Dead
Here is what most comparison content glosses over. If you search “ArkOS vs JELOS” in August 2026, you’ll find years-old forum threads still recommending both as if they’re neck-and-neck rivals. They are not.
ArkOS’s original maintainer, developer christianhaitian, posted on the project’s GitHub repository that ArkOS “will no longer be maintained effective immediately,” with the last tagged release sitting at v2.0 from July 31, 2025 — a SourceForge-hosted image weighing in at 8.8 GB and bundling PPSSPP v1.19.3, the final emulator core update the project shipped. The project’s GitHub wiki formalized the end-of-support with a December 2025 notice, and the repository is kept online for historical reference, but there has been no upstream release in over a year as of this writing. Community forks — most notably AeolusUX’s ArkOS-R3XS build for R36S-family clones, alongside a newer dArkOS successor project flagged in that same wiki update — have picked up some of the slack, but they are unofficial and maintained by volunteers on their own schedule, not the original team.
JELOS went first. The JustEnoughLinuxOS GitHub organization was archived on May 8, 2024, with a note explaining the distribution was “no longer maintained” and that the project “has come to an end.” Its last widely-cited release builds date to March 2024 (tag 20240313) and earlier. What actually happened is that JELOS’s core developers rebuilt the project under a new name — Rocknix — which continues the immutable-Linux approach on a wider device list. If you’re choosing between “JELOS or something else” today, you’re really choosing Rocknix; JELOS itself is a dead end.
muOS is the one still shipping. Its official downloads page lists a build line labeled “2601.1 Funky Jacaranda” as the current public release — muOS uses year-month style version tags, so 2601 corresponds to a January 2026 release — and it followed 2601.0, which a Retro Handhelds report identified as the project’s first major system update of 2026. The project’s Reddit and Discord communities describe updates as ongoing through mid-2026, and PortMaster’s own FAQ, current as of August 2026, lists muOS as “fully supported” among actively maintained firmwares — a direct contrast to the same FAQ’s discontinued-upstream note on ArkOS. That is the single most important fact in this whole comparison: if you want firmware that’s still receiving bug fixes and new device support in real time, muOS and Rocknix are your actual choices, not ArkOS and not the original JELOS.
Release Timeline: How Each Project Reached August 2026
Reading these dates as a single sequence makes the gap between “actively maintained” and “quietly dead” harder to miss than seeing them scattered across separate announcements. Here is every key date referenced in this comparison, lined up in order.
| Date | Event |
|---|---|
| March 13, 2024 | JELOS’s last widely-cited build tag (20240313) ships |
| May 8, 2024 | JustEnoughLinuxOS GitHub organization archived, and the core team regroups as Rocknix |
| July 31, 2025 | ArkOS’s final tagged release, v2.0, ships |
| Shortly after | Developer christianhaitian announces ArkOS “will no longer be maintained effective immediately” |
| Early 2026 | muOS ships 2601.0, its first major system update of the year, per a Retro Handhelds report |
| 2026 (current) | muOS ships 2601.1 “Funky Jacaranda,” the build listed on its official downloads page today |
Laid out this way, the pattern is hard to miss. JELOS went quiet first, sitting archived for more than two years by August 2026. ArkOS followed the same script roughly a year later, with a dated, on-the-record announcement that removed any ambiguity about its future. muOS is the only name on this list with more than one entry in 2026 itself: 2601.0 arrived first, and 2601.1 followed as the build currently listed on the project’s downloads page, with its Reddit and Discord communities describing work as ongoing into the second half of the year. A project that has already shipped two labeled updates in the current year is playing a fundamentally different game than one whose most recent tag predates the year before last.
muOS vs ArkOS vs JELOS: Full Specs Comparison
| Spec | muOS | ArkOS (original) | JELOS (original) |
|---|---|---|---|
| Maintenance status (Aug 2026) | Active | Discontinued (last release Jul 2025) | Discontinued (archived May 2024) |
| Successor project | N/A — still primary | Community forks (e.g. ArkOS-R3XS) | Rocknix |
| Base OS type | Custom Linux CFW, purpose-built | Ubuntu-based | Immutable Linux distro |
| Front end | Custom console-style menu | EmulationStation | EmulationStation-style |
| Primary chipset target | Allwinner H700, RG40XX ARM SoCs | Rockchip RK3326 / RK3566 | Rockchip RK3566 / RK3588 |
| Key devices supported | RG35XX family, RG40XX H/V, RG28XX, RG34XX, RGCubeXX, TrimUI Brick/Smart Pro | RG351P/M/MP/V, RG353P/M/V/VS, RG503, Powkiddy RGB10-30, R36S, R35S | RG353 family, RG503, Powkiddy RK2023/RGB30/X55, RGB10 Max 3, Orange Pi 5 |
| PortMaster (native game ports) | Limited | Yes, 70+ ports bundled | Yes, via RetroArch/standalone |
| Netplay | Not a headline feature | Yes, via RetroArch | Yes, via RetroArch |
| Theming | Extensive per-device theme/overlay system | EmulationStation themes | EmulationStation-style themes |
| Save states | Yes (emulator-level, standard) | Yes (emulator-level, standard) | Yes (emulator-level, standard) |
| Wi-Fi / scraping | Where hardware supports it | Where hardware supports it | Where hardware supports it |
| License / cost | Free, open source | Free, open source | Free, open source |
Note the chipset split: muOS and ArkOS barely overlap on hardware. muOS lives almost entirely on Anbernic’s H700-based RG35XX/RG40XX line plus TrimUI, while ArkOS (and its forks) targets the older RK3326/RK3566 Rockchip devices. A March 2026 R36S buyer’s guide framed the pair as close rivals, giving muOS only a “slight edge” in speed and polish and citing a roughly 5-second boot time, while a separate Retroportatil guide from June 2026 draws the line more plainly — recommending muOS for newer Anbernic models and steering RK3326/RK3566 owners (R36S, Powkiddy) toward ArkOS instead. That means the “which is better” question is often moot — your device usually only has one realistic CFW option to begin with.
Where Knulli and Rocknix Fit In
Because two of the three original contenders are effectively retired, the real 2026 comparison has to include their replacements.
Knulli is a Batocera-derived custom firmware that has been aggressively expanding its device matrix. Its changelog shows a build tagged “Scarab (20260511)” — an 11 May 2026 release — that added support for Miyoo Flip, Powkiddy X55, Powkiddy RGB30, Anbernic RG ARC-S (all RK3566-class), plus GKD Pixel 2, BattleXP G350, MagicX Xu mini-m, and R36S (RK3326-class). Knulli also has a build for Anbernic’s H700 chips (RG35XX Plus, RG35XX 2024), putting it in direct competition with muOS on that hardware — though its RG35XX Plus build was still labeled alpha and tester-only as of mid-2026, with downloads gated behind a Ko-fi support link for the developer. Community threads frame the choice on RG35XX as: muOS for a polished, turnkey console experience, Knulli for Batocera-style depth and configurability once you’re comfortable tinkering.
Rocknix is the direct continuation of JELOS, built by much of the same team, using the same immutable-partition philosophy. If you liked JELOS’s approach — atomic updates, RK3566/RK3588 focus — Rocknix is where that lineage lives now. It is the project to check for current device images rather than searching for a “JELOS 2026 download” that does not exist.
For broader context on the desktop-class end of the CFW spectrum — Batocera, RetroPie, and Recalbox running on mini PCs and Raspberry Pi rather than pocket handhelds — see our Batocera vs RetroPie vs Recalbox comparison. Batocera itself shipped version 43 “Glasswing” on May 8, 2026, with a 43.1 point release on May 30, and it remains the reference point most handheld CFWs are measured against for netplay, scraping, and controller support.
Device Compatibility: Which Firmware Fits Your Handheld
| Device / Chipset | Best current CFW | Notes |
|---|---|---|
| Anbernic RG35XX Plus / 2024 / H / SP / Pro | muOS | Knulli alpha also available, tester-only |
| Anbernic RG40XX H / V, RGCubeXX, RG28XX, RG34XX | muOS | Primary supported device family |
| TrimUI Brick / Smart Pro | muOS | Official muOS device tier |
| Anbernic RG351 / RG353 series, RG503 | ArkOS fork or Rocknix | Original ArkOS discontinued; check ArkOS-R3XS or Rocknix builds |
| Powkiddy RGB10 / RGB20 / RGB30 | ArkOS fork or Rocknix | Rocknix has broader active support in 2026 |
| R36S / R35S / RK3326 clones | Knulli or ArkOS-R3XS fork | Knulli’s Scarab build added R36S support in May 2026 |
| Miyoo Flip, Powkiddy X55, RG ARC-S | Knulli | Added in Knulli Scarab (20260511) |
| Powkiddy RK2023, RGB10 Max 3 | Rocknix | Direct JELOS successor hardware |
| Steam Deck, mini PCs, x86 hardware | Batocera or Bazzite | Outside the handheld-CFW category entirely |
SoC Fragmentation: Why One Firmware Can’t Rule Them All
The device-compatibility table above isn’t arbitrary. It maps directly onto which chipmaker built the silicon inside each handheld. Anbernic’s newer RG35XX Plus, RG35XX 2024, RG40XX H/V, RG28XX, and RG34XX models all run on Allwinner’s H700 chip, while the older RG351 and RG353 lines, the RG503, and most Powkiddy and R36S-style clones run on Rockchip’s RK3326 or RK3566 silicon instead. Allwinner and Rockchip are separate fabless chip designers, not two versions of the same product line, and that distinction is the real reason muOS and the ArkOS/JELOS lineage never had to compete head-to-head for the same hardware.
Porting a custom firmware from one chip family to another isn’t a recompile. It’s closer to a rewrite. Each SoC vendor ships its own Linux kernel fork bundled with its own drivers for the GPU, video decoder, and power-management blocks, and very little of that low-level code carries over between an Allwinner part and a Rockchip one. A firmware team that has spent years tuning boot scripts, CPU governor profiles, and display drivers around Rockchip’s RK3566 has to start substantially over to support Allwinner’s H700 properly. That’s a large part of why Knulli’s own H700 build for the RG35XX Plus was still labeled alpha and gated behind a developer support link as of mid-2026, even with its RK3326/RK3566 support already mature.
It’s also why “which firmware wins” rarely has one answer in this category the way it might for, say, competing web browsers. muOS didn’t out-compete ArkOS on features so much as it grew up on entirely different silicon, and Rocknix inherited JELOS’s RK3566/RK3588 territory rather than expanding into Anbernic’s H700 devices. The practical upshot for buyers is the same point this guide keeps returning to: identify your handheld’s chipset first, since that alone eliminates most of the field before “which firmware is better” ever becomes a relevant question.
Installation and Setup: How Hard Is Each One?
All four projects (muOS, ArkOS/forks, Knulli, Rocknix) follow the same basic install pattern that’s become standard across the retro handheld scene: download the correct image for your exact device model, flash it to a microSD card with a tool like Raspberry Pi Imager or balenaEtcher, insert the card into the device’s secondary card slot (most Anbernic devices have two), and boot. The firmware then handles first-run setup — expanding the partition, generating the ROM folder structure, and prompting for Wi-Fi and region settings.
muOS is generally considered the most beginner-friendly of the group because it targets a narrow, well-documented device list and its official site (muos.dev) maintains a single canonical devices page rather than scattering instructions across wikis and forum threads. ArkOS forks and Rocknix require more comfort navigating GitHub release pages, since neither has a single unified “download this” button the way muOS does — you need to identify your exact SoC and clone variant first. Knulli sits in between: its official device matrix at knulli.org is clean and current, but some builds (like the RG35XX Plus alpha) are gated behind developer support links rather than open downloads.
A note on tooling: Raspberry Pi Imager, originally built for Raspberry Pi SD cards, has become the de facto flashing tool across this entire scene because it handles compressed image formats (.img.gz, .img.xz) without requiring a separate decompression step, verifies the write automatically, and runs identically on Windows, macOS, and Linux. balenaEtcher remains a solid alternative with a friendlier interface for first-timers, though it’s slower on large images. Whichever tool you use, always eject the SD card properly rather than pulling it immediately after the write finishes — a truncated write is one of the most common causes of a handheld that boots to a black screen on the first attempt.
If you’re setting up a Steam Deck or ROG Ally-class handheld rather than a budget Anbernic device, the installation process looks different — see our guide on how to install SteamOS on ROG Ally or PC for that separate workflow.
Performance and Emulation Compatibility
None of these projects publish standardized cross-platform benchmarks, and comparing “performance” across muOS, ArkOS, and JELOS is somewhat apples-to-oranges since they largely target different hardware. What can be said with confidence:
- All four (muOS, ArkOS, Knulli, Rocknix) build on the same underlying emulator cores — RetroArch plus standalone emulators like PPSSPP and DuckStation — so raw emulation accuracy for a given system (say, PS1 or Game Boy Advance) is nearly identical across firmware when running on the same chipset.
- Where firmware choice actually changes performance is overhead: how much RAM and CPU the front-end menu itself consumes, how quickly the device boots to the game list, and how well the firmware manages CPU governor/clock speed profiles per emulator.
- muOS is frequently described by the RG35XX community as tightly tuned for its supported hardware, since it targets a narrow device list rather than spreading development across dozens of SoCs.
- Knulli, being Batocera-derived, inherits Batocera’s broader but more generalized performance tuning rather than per-device optimization.
- Batocera 43 (the desktop-class reference point) updated several emulator cores in its May 2026 release, including Cemu to an April 2026 build and BigPEmu to v121 — a reminder that emulator core versions, not just the wrapping OS, drive a meaningful share of compatibility improvements each year.
For a broader look at emulator accuracy scores across PC-class systems (PS2, PS3, and beyond) rather than handheld firmware, see our Best Emulators for PC comparison.
Community and Development Activity
Feature lists only tell part of the story with volunteer-maintained firmware — the real signal is whether anyone is actually behind the wheel. muOS keeps an active presence across Reddit’s r/RG35XX community, a dedicated Discord server, and its own community forum at community.muos.dev, where the project posts changelogs and roadmap updates directly rather than leaving users to reverse-engineer release notes from GitHub diffs. That level of direct communication is part of why muOS is so often the default recommendation handed to first-time RG35XX buyers: there’s a clear, current place to ask questions and get an answer from someone who actually maintains the code.
Knulli and Rocknix both publish structured changelogs on GitHub with dated build tags — a habit inherited from Batocera and JELOS respectively — which makes it straightforward to verify whether a project is still active without digging through forum hearsay. That transparency matters more in this niche than in most software categories, because the cost of guessing wrong is a bricked SD card and a wasted evening. ArkOS’s discontinuation notice, by contrast, is a useful example of the opposite: a clear, dated statement from the maintainer that removed any ambiguity about the project’s future, even if the news itself was disappointing for existing users.
The practical takeaway when you’re evaluating any custom firmware, on any device, is to check three things before you commit an evening to a flash: the date of the most recent tagged release on GitHub, whether the project’s own documentation site (not a third-party wiki) has been updated in the current year, and whether the community forum or subreddit shows posts from the maintainer within the last few months rather than just users troubleshooting each other’s problems.
How Long Is Too Long? A Framework for Spotting Abandoned Firmware
Most buyers don’t realize a project is dead until they hit a wall: a controller that won’t calibrate, a save state that won’t load, a device revision the firmware never learned to support. By then the evening is already lost. A better habit is to check maintenance status the way you’d check a used car’s service record, before committing rather than after. Lined up side by side, muOS, ArkOS, and JELOS make a useful case study for judging any custom firmware project, not just these three.
ArkOS is the clean example of a confirmed death. The moment developer christianhaitian posted that the project “will no longer be maintained effective immediately,” there was nothing left to guess. A dated, explicit statement like that beats months of silence every time, and it landed alongside a final tagged release of v2.0 on July 31, 2025 — putting ArkOS at more than a year without an upstream update as of August 2026. JELOS is the slower version of the same story. Its GitHub organization was archived on May 8, 2024, which by August 2026 works out to more than two years of silence, well past the point where a buyer should keep hoping for a comeback.
- A dated abandonment statement, like ArkOS’s, is the strongest signal available. Treat it as final rather than waiting for a surprise update that isn’t coming.
- An archived GitHub organization, like JELOS’s, is nearly as strong. GitHub disables new issues and pull requests on archived repos, a deliberate setting the maintainers chose, not an accident of neglect.
- Silence with no dated statement and no archive flag is the gray area. Check the project’s subreddit or Discord for posts from the actual maintainer, not just users troubleshooting each other, before assuming the worst.
- A project still shipping dated builds, like muOS’s 2601.1 release (nicknamed “Funky Jacaranda,” following 2601.0 earlier in the year), is the clearest sign of life, since someone has to actively package and publish that build on a real schedule.
Theming, UI, and Customization Compared
The visual experience differs more than the underlying emulation does. muOS built its own menu system from scratch rather than relying on EmulationStation, which gives it a distinctly console-like feel — closer to a first-party PlayStation or Switch menu than a PC file browser. Its theme system supports device-specific overlays (bezels shaped for the RG35XX’s screen dimensions versus the RG40XX’s, for example), font scaling, and grid or list-based game browsers that can be swapped without touching configuration files directly.
ArkOS, Knulli, and Rocknix all lean on EmulationStation or an EmulationStation-derived front end, which trades some of that native polish for a much larger existing theme ecosystem — years of community-made EmulationStation themes, originally built for RetroPie and Batocera, generally drop in with minimal modification. If you already have a theme you love from a Batocera or RetroPie box, it’s more likely to be portable to Knulli or an ArkOS fork than to muOS, simply because they share the same front-end technology.
Box art scraping — pulling cover art and metadata for your ROM library automatically — works differently across the group as well. EmulationStation-based firmware (ArkOS, Knulli, Rocknix) typically ships a built-in scraper that talks to community art databases directly from the device, provided you have Wi-Fi configured. muOS’s approach is less centralized in the current build line, and many users instead scrape locally on a PC using a tool like Skraper or SteamGridDB before copying the resulting images over, which adds a step but avoids relying on the handheld’s often-slow onboard Wi-Fi radio for large downloads.
Pricing: All Free, But Hardware Costs Vary
Every firmware discussed here is free and open source — there is no license fee for muOS, ArkOS, JELOS, Rocknix, or Knulli. The real cost consideration is the handheld hardware itself, and that market has been squeezed by the 2026 DRAM shortage that pushed component costs up across the board.
| Device class | Typical price (Aug 2026) | Recommended CFW |
|---|---|---|
| Anbernic RG35XX Plus / SP | $60-$80 | muOS |
| Anbernic RG40XX H / V | $70-$90 | muOS |
| TrimUI Brick | ~$60 | muOS |
| R36S / R36MAX clones | $45-$65 | Knulli or ArkOS fork |
| Anbernic RG353 series | $90-$130 | Rocknix or ArkOS fork |
| Powkiddy RGB30 | $100-$120 | Rocknix or Knulli |
Our coverage of the handheld RAM crisis that forced AYANEO to halt shipments explains why several handheld makers have raised prices or paused new SKUs in 2026 — worth reading before you commit to a specific device.
Because the firmware layer is free regardless of which project you choose, the only real “cost” comparison worth making is opportunity cost: buying a device with strong active firmware support (muOS-class Anbernic hardware, or a Knulli-supported RK3566 clone) versus buying a cheaper device that only ever had ArkOS or JELOS support and now has nothing actively maintained behind it. A handheld that’s $15 cheaper but stuck on year-old, bug-riddled firmware is rarely the better deal once you factor in the hours spent troubleshooting instead of playing.
Five Real-World Use Cases
1. You just bought an Anbernic RG35XX Plus and want it working today. Go straight to muOS. It’s the officially supported, actively updated option for that exact device, with a single canonical download page and no need to hunt through forks.
2. You own an older RG351 or RG353 and were told to install ArkOS. Skip the original ArkOS repo — it hasn’t shipped a release since July 2025. Look for the ArkOS-R3XS community fork or, better, check whether Rocknix has a build for your exact model, since Rocknix is under more active development.
3. You’re setting up an R36S-style clone and want the newest device support. Knulli’s May 2026 Scarab build specifically added R36S support, alongside newer devices like Miyoo Flip and Powkiddy RGB30. It’s the most actively expanding project on RK3326/RK3566 hardware right now.
4. You want Batocera-style depth and configurability on a handheld. Knulli is literally Batocera-derived, so if you’re coming from a Batocera box and want that same service-based configuration model on a pocket device, it’s the closest match.
5. You found an old JELOS download link in a 2023 forum post. Don’t use it. The project is archived and unmaintained. Go to Rocknix instead — same team, same immutable-OS philosophy, active builds for the same RK3566/RK3588 hardware.
6. You’re buying your first retro handheld and don’t want to think about firmware at all. Pick a currently-shipping Anbernic RG35XX Plus or TrimUI Brick specifically because muOS supports it out of the box with a single well-documented install path — the device and firmware pairing matters more than either spec sheet in isolation for a first-timer.
7. You want Wi-Fi-based box art scraping without hooking your handheld up to a PC. Lean toward an EmulationStation-based option — Knulli, Rocknix, or an ArkOS fork — since their built-in scrapers pull cover art and metadata directly over Wi-Fi, where muOS more commonly requires scraping on a computer first and copying the images over.
Common Setup Problems and How to Avoid Them
Most of the frustration people run into with retro handheld firmware isn’t a bug in the OS itself — it’s a mismatch between the image they downloaded and the exact hardware revision they own. Anbernic in particular has shipped multiple silent hardware revisions under the same model name (the RG35XX and RG35XX Plus each have more than one board revision in the wild), and flashing the wrong image can leave you with a black screen, no audio, or broken analog stick input. Before downloading anything, check the tiny revision markings on your device’s board or box, and cross-reference against the firmware project’s device page rather than assuming “RG35XX” means one single thing.
The second most common issue is SD card quality. Budget handhelds are notoriously picky about card speed class, and a slow or counterfeit card can produce symptoms that look exactly like a corrupted firmware image — stuttering audio, games that won’t launch, or the device hanging on the boot logo. Buying a card from a reputable brand rated at least UHS-I U3 or A2, and formatting it fresh with the tool the firmware project recommends (rather than reusing a card that previously held a different CFW) resolves a large share of “my install is broken” reports across every project covered here.
Finally, don’t skip the changelog. Because muOS, Knulli, and Rocknix are all under active development, upgrading from one build to the next occasionally changes a folder structure or configuration file format. Jumping several versions at once without reading the notes in between is the single most common cause of lost save files reported in each project’s support channels — updating incrementally, or at minimum backing up your saves before any update, avoids the problem entirely.
What You Actually Lose by Staying on Dead Firmware
It’s tempting to shrug off an abandoned project with “it still works, why switch?” For a single-player emulation handheld, that’s often true right up until it isn’t. The real cost of unmaintained firmware shows up gradually, not all at once.
RetroArch and its standalone emulator cores keep shipping accuracy and compatibility fixes on their own release schedule, independent of whatever firmware wraps around them. An active project like muOS or Rocknix pulls those core updates forward to users on a regular cadence. A frozen project like the original ArkOS or JELOS is stuck on whatever core versions were current when its last build shipped, which means fixes and additions made to RetroArch since July 2025 or May 2024 never reach a device still running one of those old images.
There’s also a hardware ceiling to consider. Anbernic, Powkiddy, and their peers keep releasing new board revisions under familiar model names, and only an actively maintained firmware can add the driver tweaks or quirks-handling a new revision needs. That’s the real argument for the migration steps below: it isn’t about chasing new features for their own sake, it’s about staying inside a project that can still respond when a new device revision or a newly discovered bug shows up.
Migration Guide: Moving From ArkOS or JELOS in 2026
If you’re currently running an old ArkOS or JELOS install and want to move to an actively maintained option, here’s the process:
- Back up your saves and states first. On both ArkOS and JELOS, save files typically live in a dedicated
savesoruserdatafolder on the SD card’s data partition — copy that folder to your PC before doing anything else. - Identify your exact chipset and model. Rocknix and the ArkOS forks are organized by specific device codename (not just “RK3566”), so check your device’s exact model number against the project’s device compatibility page before downloading.
- Download the current build from the successor project — Rocknix’s GitHub releases for former JELOS hardware, or the relevant ArkOS fork’s releases page for RK3326/RK3566 devices.
- Flash to a fresh SD card rather than overwriting your existing one, so your old firmware remains a fallback if something goes wrong.
- Restore your saves by copying the backed-up save folder into the equivalent directory on the new firmware — folder structures are usually similar but not always identical, so check the new project’s documentation for exact paths.
- Re-scrape box art and rebuild your game list since most CFWs don’t share a scraping database across projects.
- Test controller mapping and Wi-Fi before deleting your old SD card backup, since hardware quirks (analog stick calibration, Bluetooth pairing) sometimes need re-configuration after a firmware switch.
Pros and Cons
muOS
- Pro: Actively maintained with regular 2026 releases
- Pro: Clean, console-like UI with strong per-device theming
- Pro: Single canonical device/download page, easy for beginners
- Con: Narrow device support — Anbernic RG35XX/RG40XX family and TrimUI only
- Con: No official Miyoo or Powkiddy support
ArkOS (original)
- Pro: Broad legacy device support across RK3326/RK3566 hardware
- Pro: Bundled PortMaster support for 70+ native game ports
- Con: Discontinued since July 2025 — no upstream updates
- Con: Depending on unofficial forks for anything current
JELOS (original)
- Pro: Pioneered the immutable-OS approach for handheld CFW
- Con: Archived since May 2024 — do not download for new setups
- Con: Superseded entirely by Rocknix, which few beginner guides mention by name
Knulli
- Pro: Fastest-growing device matrix of the group, adding new hardware every few months
- Pro: Batocera-derived depth and configurability for advanced users
- Pro: Covers both RK3326 and RK3566-class devices plus some Anbernic H700 hardware
- Con: Some device builds (RG35XX Plus) remain alpha and tester-gated
- Con: Less beginner-polished than muOS’s turnkey approach
Rocknix (JELOS’s successor)
- Pro: Direct continuation of JELOS’s immutable-OS design, built by much of the same team
- Pro: Actively maintained for RK3566/RK3588 hardware where original JELOS left off
- Con: Name recognition lags behind JELOS’s, so many older guides don’t mention it
- Con: Device list still catching up to what JELOS supported at its peak
The Verdict
If your device is an Anbernic RG35XX, RG40XX, or a TrimUI Brick/Smart Pro, install muOS. It is the only one of the three original contenders still under active development in August 2026, it has a single well-documented device list, and its console-style interface is the easiest of the group to hand to a non-technical family member.
If your device runs an older Rockchip RK3326 or RK3566 chip — an R36S clone, an Anbernic RG353, or a Powkiddy RGB30 — do not chase the original ArkOS or JELOS downloads. Both are dead ends. Look at Rocknix first for the closest continuation of JELOS’s approach, or Knulli if you specifically want its Batocera-derived feature depth and your device made it into the May 2026 Scarab release. Community ArkOS forks like ArkOS-R3XS remain a fallback for hardware neither of those two has picked up yet.
The single number that matters most in this comparison: of the three firmware projects most beginner guides still recommend as if they’re equally current, only one — muOS — shipped a new release in 2026. That’s the filter to apply before following any older tutorial you find.
One last piece of practical advice: bookmark the actual project pages — muos.dev, knulli.org, and the Rocknix GitHub releases page — rather than saving a specific YouTube tutorial or forum thread. Firmware projects in this space change fast enough that a video from even six months ago can point you toward a build that’s since been superseded, a device page that’s been reorganized, or, in ArkOS and JELOS’s case, a download link for a project that no longer exists in any actively maintained form. The names in this comparison will likely look different again in another year, but the method for evaluating them — check the maintenance status before the feature list — will not.
Frequently Asked Questions
Is ArkOS still being updated in 2026?
No. The original ArkOS project, maintained by developer christianhaitian, announced it would no longer be maintained, with its last tagged release being v2.0 on July 31, 2025. Community forks like AeolusUX’s ArkOS-R3XS continue independently, but there has been no official upstream release since mid-2025.
What happened to JELOS?
JELOS (Just Enough Linux OS) was archived on GitHub on May 8, 2024. Its core development team moved the project forward under a new name, Rocknix, which continues to support much of the same RK3566/RK3588 hardware using the same immutable-Linux design.
Is muOS built on Rocknix?
No. muOS is a separate, independently developed custom firmware with its own codebase and device list. The Rocknix lineage traces back to JELOS, not to muOS. Any similarities between the two come from both being Linux-based emulation front ends built on the same open-source emulator cores, not from a shared codebase.
Which firmware supports the most devices?
Among actively maintained projects, Knulli has been expanding its device matrix fastest, adding support for Miyoo Flip, Powkiddy X55, Powkiddy RGB30, Anbernic RG ARC-S, R36S, and several other clones in its May 2026 Scarab build. muOS covers a narrower but deeply supported list centered on Anbernic’s RG35XX/RG40XX family and TrimUI handhelds.
Can I run muOS on an R36S or Powkiddy device?
No. muOS officially targets Anbernic’s H700-based RG35XX/RG40XX chips and TrimUI’s Brick/Smart Pro, not the RK3326/RK3566 Rockchip chips found in R36S clones and most Powkiddy devices. For those devices, look at Knulli, Rocknix, or an ArkOS community fork instead.
Do I need to pay for any of these custom firmware projects?
No, all of them — muOS, ArkOS, JELOS, Rocknix, and Knulli — are free and open source. Some Knulli device builds, such as its RG35XX Plus alpha, are gated behind a developer support link (like Ko-fi) as a courtesy to the maintainer, but the underlying firmware itself is not sold.
What’s the difference between custom firmware and something like Batocera or EmuDeck?
Batocera and EmuDeck target different hardware classes. Batocera runs on PCs, mini PCs, and full-size devices like Steam Deck, while EmuDeck is an emulator installer layered on top of an existing OS (typically SteamOS or Windows) rather than a firmware replacement. muOS, ArkOS, JELOS/Rocknix, and Knulli specifically replace the stock firmware on budget pocket handhelds under $150.
Will switching custom firmware delete my save files?
Not if you back them up first. Because most CFWs use a similar folder structure for save files, you can usually copy your saves and RetroArch save states off the old SD card and manually place them in the equivalent folder on the new firmware, though exact paths vary by project — always check the new firmware’s documentation before overwriting anything.
Does Knulli replace Batocera on handhelds?
Not exactly — Knulli is derived from Batocera’s codebase and shares its service-based configuration philosophy, but it’s packaged and tuned specifically for pocket handhelds like the RG35XX, R36S, and Miyoo Flip. Batocera itself remains the go-to choice for PCs, mini PCs, and larger devices like Steam Deck, while Knulli is the handheld-focused branch of that same lineage.
Should I wait for a new ArkOS or JELOS release before buying a handheld?
No. Both projects are discontinued in their original form, and there’s no indication either will resume upstream development. Buy based on which actively maintained firmware — muOS, Knulli, or Rocknix — supports your target device today, rather than waiting on a project that has already told its community it’s done.
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