Frosted OS is an Open Source POSIX Operating System for Cortex-M Micro-controllers
Frosted, which stands for “Free Operating Systems for Tiny Embedded Devices”, is an OS with a POSIX-compliant system call API, borrowing the Linux kernel kconfig for configuration, and currently supporting ARM Cortex M0,M3,M4, and M7 MCU including Texas Instruments Stellaris LM3S, STMicro STM32F4/F7, and NXP LPC17XX micro-controllers. The developers are focusing on IoT applications, as well as porting retro-games such as Doom.
The Wiki explains how to build and run the OS on either Qemu (in a Linux computer) used LM3S target, or an STM32F4 Cortex -M4 or STM32F7 Cortex-M7 board. The team also uploaded showing a video of Doom (fdoom) running on STM32F7 board, and possibly adapted from stm32doom port.
If you are interested in joining the project you can contact the developers on #frosted IRC channel, or use Github’s issues tab to report bugs and/or new features requests. There’s also a webpage here.
Thanks to Zoobab for the tip.