This is pretty neat. Some researchers at MIT CSAIL have cooked up a device which turns a manual router into handheld CNC. The existing tool sits within a mechanism which allows a human to move it around on the work piece. Using a camera and some positioning tags, the device uses its internal actuators to move the tool in the correct fine pattern while the human moves it in a coarse pattern around the piece. How cool!
http://www.alecrivers.com/positioncorrectingtools/