Freedom251 › Emulation Frontends
MustardOS
What MustardOS is
MustardOS, also called muOS, is free custom firmware primarily for handheld gaming devices. It offers emulation, controller navigation, portable mode, and configuration options for changing appearance, style, and behavior. Supported devices include handhelds from Anbernic and TrimUI, including RG35XX models, RG28XX H, RG34XX H and SP, RG40XX H and V, RGCUBEXX, TrimUI Brick, and TrimUI Smart Pro. Documentation lists systems and cores such as RetroArch and ScummVM. Installation requires writing a MustardOS image to an SD card with an image-flashing tool, then inserting that card into the handheld. For local file access, users can enable SFTP and Filebrowser and open Filebrowser in a browser on the same network; the guide lists muos as both default username and password. Syncthing can copy the save folder to a PC for backup, but Watch for Changes works only on FAT32 and should be disabled for exFAT. Support is offered through Discord and a community forum.
Who it suits
It suits handheld owners who want configurable firmware and emulation features, whether new to handhelds or experienced enthusiasts. Users should check device support and follow the SD-card installation process.
What it does well
- Free custom firmware
- Supports Anbernic and TrimUI handhelds
- Includes RetroArch and ScummVM cores
- Offers themes and behavior customization
What to know first
- Installation requires flashing an SD card
- Syncthing Watch for Changes requires FAT32
- Default Filebrowser credentials are publicly documented
Limits
MustardOS is free. Syncthing's Watch for Changes option works only on FAT32 partitions and should be disabled for exFAT; Filebrowser access requires SFTP plus Filebrowser to be enabled.
Plans
| Plan | Billed and limits | Price |
|---|---|---|
| Hero | $12 per month · nightly development exclusives · name on credits screen · special Discord access · behind the scenes | $12 a month |
| Artificer | $6 per month · testing crew preview access · weekly testing updates · special Discord access | $6 a month |
| Knight | $9 per month · exclusive testing group · weekly testing updates · name on credits screen · special Discord access | $9 a month |
As muos.dev lists them, read 7 Oct 2026. The maker's own page has the final word.
Getting started
- Visit https://muos.dev/
- Use an image flashing tool to write MustardOS to an SD card
- Insert the SD card into a supported handheld
- Enable SFTP plus Filebrowser for local browser access
- Use Syncthing to sync the save folder to a PC if needed
Verdict
MustardOS provides configurable, free firmware with broad listed handheld support and emulation features. Installation, file-access setup, and the FAT32 limitation are practical details to consider before use.
Questions
What devices does MustardOS support?
The listed devices include Anbernic RG28XX H, RG34XX H and SP, RG35XX models, RG40XX H and V, RGCUBEXX, TrimUI Brick, and TrimUI Smart Pro.
Is MustardOS free?
Yes. MustardOS has a free plan.
How is MustardOS installed?
Write the MustardOS image to an SD card with an image flashing tool, then insert the card into the handheld.
Which emulation systems or cores are documented?
The documentation lists supported systems and cores including RetroArch and ScummVM.
How can files be accessed locally?
Enable SFTP plus Filebrowser, then open Filebrowser in a browser on the same local network. The default username and password are both muos.
Where can users get support?
The project points users to its Discord and community forum for assistance.
Facts from MustardOS's own pages
- Audience
- MustardOS says it is designed for both people new to handhelds and experienced enthusiasts. · muos.dev, 7 Oct 2026
- Default credentials
- The Filebrowser guide gives the default username and password as muos and muos. · muos.dev, 7 Oct 2026
- Device support
- The supported-device page lists handhelds from Anbernic and TrimUI, including RG35XX and TrimUI Smart Pro models. · muos.dev, 7 Oct 2026
- Emulation
- The documentation lists supported systems and cores including RetroArch and ScummVM. · muos.dev, 7 Oct 2026
- File access
- The built-in Filebrowser can be accessed through a browser on the same local network after enabling SFTP + Filebrowser. · muos.dev, 7 Oct 2026
- Funding
- The project accepts one-off donations and subscriptions to support software, hardware, and development accessories. · muos.dev, 7 Oct 2026
- Installation
- Installation uses an image flashing tool to write MustardOS to an SD card, which is then inserted into the handheld. · muos.dev, 7 Oct 2026
- Personalization
- The firmware is configurable and themeable, with options to customize its look, style, and behavior. · muos.dev, 7 Oct 2026
- Product
- MustardOS (muOS) is custom firmware primarily for handheld devices. · muos.dev, 7 Oct 2026
- Project origin
- The site describes MustardOS as having begun as a small personal hobby project that grew into a community project. · muos.dev, 7 Oct 2026
- Project team
- The crew page identifies XongleBongle as the lead developer behind MustardOS. · muos.dev, 7 Oct 2026
- Storage caveat
- The Syncthing guide says its Watch for Changes option works only on FAT32 partitions and should be disabled for exFAT. · muos.dev, 7 Oct 2026
- Support
- The site points users to its Discord and community forum for assistance. · muos.dev, 7 Oct 2026
- Sync and backup
- The Syncthing guide describes syncing the MustardOS save folder to a PC as a backup method. · muos.dev, 7 Oct 2026
Where MustardOS stands on Freedom251
- Emulation Frontends#16 of 25