Mike McCracken, loneconspirator , has made an Audio ping-pong game (or audio Pong, really) for one person using an Arduino board, headphones, and an accelerometer (a sensor that measures tilt, used in the Nintendo Wii controller). It is still in an early prototype stage, but I have a feeling he will keep refining it.
It is a one-person game. You put on the headphones, and you will hear a sound “approaching”. It will be to your right or left, and you tilt your head to center the sound. If you tilt your head, or the “paddle”, to the right position, you strike the “ball”, and it will come back. Speed increases over time, just like classic arcade games.