|This is a nice little particle system where marbles bounce around a box and collide off each other and stationary objects. Yes I know marbles don't bounce but I named it that befor I put in the bouncing so its a bit late to change it :P
All collisions are 100% elastic so no momentum is ever lost. You can turn gravity on and off and do some other things like wireframe and even follow one marble as it bounces round. It was completed in late august 2003 for uni, and I haven't really looked at it since!