The Microsoft Kinect is a games controller that tracks movement.
It is relatively straightforward to use this to control music, and in doing so, create a motion-to-music device using Synapse or Max for Live with Ableton Live.
Kinect has the potential to be a very cheap accessible musical interface, and can be superb. However setting up the tracking can be fiddly and unreliable.
We are working on a guide and video, but for now have a look at Synapse.