Headtracking2 is a demo based on the second half of Johnny Chung Lee's head tracking demo. The demo displays a set of targets at different screen depths. As the user moves his head, the demo tracks this movement and adjusts the display's projection matrix such that the targets appear to float in space. A Wii implementation of the first part of Johnny's demo can be found here.
To use, place your first Wiimote on your TV facing you. Move the sensor bar around in front of you.