FRANK OS is a complete desktop operating system for the RP2350 microcontroller that squeezes a mouse-driven windowed GUI, a file manager, a terminal, and a library of applications into just 520 KB of SRAM. Built by Mikhail Matveev and licensed under GPL-3.0, the project turns a chip that costs roughly $4 into something that looks and behaves like a 1990s PC, running at 640x480 at 60 Hz with a 16-color palette over DVI output.
The operating system runs on FreeRTOS with a dual-core split: Core 0 handles the UI, input processing, and application tasks, while Core 1 is dedicated entirely to real-time DVI scanline rendering via the DispHSTX driver. The desktop includes overlapping windows with drag and resize support, a taskbar with a system tray and clock, an Alt+Tab switcher, and a Start menu that scans an SD card for installed applications at boot. The window manager supports up to 16 simultaneous windows with proper z-order stacking.
FRANK OS ships with 9 standalone applications loaded from SD card as ARM ELF binaries. The lineup includes a Notepad with C syntax highlighting and a built-in compiler, Solitaire, Minesweeper, a port of the 1983 arcade game Digger, a full ZX Spectrum 48K emulator with Z80 emulation running via ARM Thumb-2 assembly, an MP3 player styled after WinAmp 2.x, and an MMBasic interpreter. The terminal runs PShell, which supports file operations, a vi editor, tar archives, and can launch compatible applications from Murmulator OS 2. Applications use a stable syscall API through a fixed-address sys_table, so binaries remain compatible across firmware updates without recompilation.
The OS targets the FRANK M2 development board, an RP2350B-based design with PS/2 keyboard and mouse ports, a DVI connector, SD card slot, and optional QSPI PSRAM for application memory. The CPU clock is adjustable between 252, 378, and 504 MHz from the Control Panel. Hard fault crash dumps are written to uninitialized SRAM and survive warm resets for post-mortem debugging. The source code and documentation are available on GitHub under GPL-3.0.
