Sponc is the best multitouch pong there is. You control position, angle and size of your bat with two fingers. The smaller you make your bat, the faster the ball bounces off it.
The initial version was written by Martin Heistermann and friends on the 11.8.2007 for the 23 hour coding contest of the c-base at the Chaos Communication Camp 2007. Needless to say, they won the contest. Since then, Archimedes Exhibitions have contributed some enhancements.
Sponc is Open Source and licensed under the GPL. You can get the source code using
git clone https://github.com/libavg/mtc-sponc.git
There is an Ubuntu package for Sponc.
Sponc can use quadro sound output - see the SponcAudio page.
More info at http://www.sponc.de.