We have ported FreeRTOS past year, you can look at these links:
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1256745982/0
The versión 0.1 Alpha (for the 0017 IDE) is available here:
http://www.multiplo.org/duinos/wiki/index.php?title=Main_Page
And there is a v0.2 Alpha which runs in 0018 at:
http://novell.chel.ru/get.php?file=DuinOS_v0.2_Alpha
We did not make the v0.2, but are working in the v0.3.
Regards,
Julián