I have posted a new version of ChibiOS/RT as ChibiOS20130529.zip http://code.google.com/p/rtoslibs/downloads/list.
This version is compatible with the new malloc in Arduino 1.05.
The ChibiOS_AVR library supports AVR Arduinos. The ChibiOS_ARM library supports the Due Arduino, and Teensy 3.0.
ChibiOS/RT microkernel features:
Static architecture, everything is statically allocated at compile time
Best in class context switch performance
128 priority levels
Round-robin scheduling for threads at the same priority level
Mutexes with support for the priority inheritance algorithm
Synchronous and asynchronous Messages
Event flags and handlers