I have posted a new version of NilRTOS as NilRTOS20130520.zip http://code.google.com/p/rtoslibs/downloads/list.
This version is compatible with the new malloc in Arduino 1.05.
NilRTOS is a very small Real-Time OS for avr Arduinos:
NilRTOS is a tiny fast RTOS written by Giovanni Di Sirio, the author of ChibiOS/RT.
"Smaller than ChibiOS/RT, so small it's almost nil."
NilRTOS runs on AVR Arduinos and is the best choice for Uno.
Fast and small on AVR Arduinos Static architecture, everything is statically allocated at compile time Preemptive multithreading Counting semaphores with timeouts Flexible FIFO class Efficient analogRead() that sleeps during ADC conversion API access from interrupt handlers Tiny unbuffered NilSerial as an alternative to Arduino Serial