It's the classic amusement arcade game Whac-a-Mole on a wall -- any normal wall, with an overhead projector and Kinect (on the floor in front of the wall, pointed upwards).
Done as an exercise to learn Processing and check out what Kinect hacking is all out. Fun!
See video at http://www.youtube.com/watch?v=mZ30Kuk4kAE
