LEJOS OSEK version 1.06 was just released. LEJOS OSEK is an open source firmware for LEGO MINDSTORMS NXT focused on high speed real-time control applications for the NXT. You can read more and download it here.

A nice feature is the Embedded Coder Robot NXT which allow you to create MATLAB(tm) and Simulink(tm) code (both from the MathWorks company) and compile it into the NXT.