CooCox CoOS is an Embedded RTOS specially for ARM Cortex-M3. It is completely open and free.
CoOS Features:
* Free and open real-time Operating System
* Specially designed for Cortex-M3
* Accords with CMSIS
* Supports preemptive priority and round-robin
* Scalable
* Interrupt latency is 0
* Can avoid priority inversion
* Stack overflow detection option
* Semaphore, Mutex, Flag, Mailbox and Queue for communication & synchronisation
* Supports the platforms of ICCARM, ARMCC, GCC
You can download code, examples and user's guide at : http://www.coocox.com/CoOS.htm