Simple, open-source, cross-platform software for mobile robotics research.
We use MOOS on all of our robots and applications including the robot car. It allows us to develop and test our autonomy system in a modular way on multiple machines across multiple operating systems.
MOOS is free, open source, cross platform software written and used by members of the Mobile Robotics Group. MOOS has its own web page which can be found at http://www.robots.ox.ac.uk/~pnewman/TheMOOS.
If you are looking for lightweight middleware designed for use in a research environment you could do a lot worse than setting the MOOS loose.