Bowntz
Bowntz is a little world of colliding circles, implemented in Haskell using OpenGL for video and SuperCollider3 for audio. Its simulation algorithm is based on directly calculating the time until the next collision rather than stepping through time at a constant rate.
Bowntz source code repository at Gitorious
Bowntz source code repository at code.mathr.co.uk
git clone http://code.mathr.co.uk/bowntz.git