It's a personal microkernel project designed as a learning ground.
Free cooperative operating system designed for microcontrollers
Free real-time operating system designed for microcontrollers
PRTOS is a simple, compact preemptive RTOS for embedded systems
Small real time operating system for AVR and ARM microcontrollers
Embedded Operating System
Tiny operating system for running HCFSM-based systems
The collection of all important commands in a single script (LINUX)
PrimOS is a 32bit multi-task OS, which is still under development.