ECU using the MPC5634 processor o5e or Open5xxxECU is an open engine control unit (ECU) based on the state-of-the-art 32 bit Freescale MPC5xxx processor family. The FreeScale MPC5xxx processors give it the speed and all the connections or features you could probably ever want. It uses a DIY assembled circuit board so you only need to purchase and install the components you actually need. This design will allow the ECU to be assembled for as little as $150 for a basic application and under $500 with all features installed - while out performing commercial ECUs costing much more. Everything needed for firmware development is available for US$99
http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=TRK-MPC5634M.
The firmware is modular, understandable and maintainable.