Think Raspberry Pi, and we instantly think of Raspberry Pi OS, a branch of Debian Linux tweaked to run on the board. But the recently-released Raspberry Pi Pico eschews the traditional Raspberry Pi setup in favor of an Arm-based microcontroller. This has not deterred David Given, who has ported a Unix-like operating system to the $4 board.
A Raspberry Pi Pico running Fuzix will not be replacing your Raspberry Pi any time soon, but it is amazing to see this Unix-like OS running on such low-power hardware. Given's port of Fuzix is based upon Alan Cox's original project, which can run on hardware almost 40 years old. Fuzix provides us with a proper Unix filesystem, support for SD cards via the SPI interface, a full set of Fuzix binaries, and all of this is available via a serial console to UART0.
Right now, there is no support for flash memory, evident in the requirement of an SD card. Given says that the code for this is complete, but a bad file system will crash the dhara FTL library and that the onboard flash is too small even for the 32MB system image.
Given provides a readme full of installation instructions, which are written for experienced Unix / Linux users to follow. The easiest way to get started is to download the Fuzix binaries and format an SD card as per the readme instructions. Then flash the UF2 file to your Pico, connect up an SD card reader via the SPI interface, connect to UART0 and start using Fuzix on a $4 microcontroller.