That's the one I wanted, thanks! And it didn't crash my browser. I notice they let you download the source code. Do you think this is the sort of software an idiot like me could include in _This Week's Finds_?
There's something really appealing about this simulation - it's like having a fishbowl... much more fun than merely watching the graph of some function. You could say it's a gimmick, but if we ever try to make stuff that appeals to ordinary folks, instead of 'scientists and engineers', I think this is the kind of gimmick that could work.