ChibiOS/RT is a free and efficient RTOS designed for deeply embedded applications. It offers a comprehensive set of kernel primitives and supports many architectures: ARM7, Cortex-M0, Cortex-M3, Cortex-M4, PowerPC e200z, STM8, AVR, MSP430, ColdFire, H8S, x86.
This project is now in the research and development stage. It is intended for very small microcontrollers with a single processor and represent simple multithreading kernel what written by C language. Is planning create implementations for AVR8 and STM8, may be. Now it is suspended until better time.