There is pretty exciting bit of activity on the LinuxCNC (EMC) group -- there is a "ready to run" port of LinuxCNC that is now targeted for the BeagleBone. This is raw stuff and still in development, but it sure sounds like it's already getting to be usable.
With more polish it could be a suitable engine for 3D printers, including those that require inverse kinematics!
http://sourceforge.net/mailarchive/message.php?msg_id=30779667
More info from the source: here
