davros is a small real-time embedded operating system kernel. The current version, davros-3, is intended to run on Arm hardware like the various raspberry pi boards. It has its origins in Xinu, from Doug Comer's book Operating System Design - The XINU Approach.
davroska is an even smaller, OSEK-like kernel. I wrote it as an exercise to find out how quickly I could throw together a quick and dirty OS. davroska runs on Arm aarch32 and aarch64 CPUs, and on Cortex M. On multi-core hardware it only runs on a single core. Supported hardware: raspberry pi zero, raspberry pi 3 and bluepill STM32 boards.
Both kernels should be fairly easy to port to other hardware.
For more information, visit https://github.com/TheLancashireman/davros.