Phun, the interactive physics simulator, is now available for Mac OS X.
Be warned. If you like physics or tinkering around with things, this program could be a huge time sync sink. (I’ve been futzing with SyncML too much lately.) I was playing with it in (ugh) Windows XP last time I was in New Orleans, and Amanda informs me that what I thought was about 20 minutes was actually closer to two hours.