XMK is a preemptive multi-tasking kernel for 8bit microcontrollers.
Its goal is to provide a bare bones RTOS with a small enough footprint (RAM+ROM) to run on 8bit microcontrollers.
Open Source RTOS for 8Bit microcontrollers - Including Hitachi H8 and Atmel's AVR chips.
preview:
http://www.shift-right.com/xmk/
5/8/2003