Phun: Physics simulator

From Kevin Purdy at Lifehacker:

Phun, a free open-source, cross-platform 2D physics simulator, makes you want to pick up blocks, or maybe crayons, and learn more about the way things fall and move under pressure. Written by a Swedish graduate student, the program teaches concepts of restitution and friction, so it's great to load up with the kids, but you'll probably find yourself sneaking a few turns by yourself at creating, and knocking over, shapes and lines. Phun is a free download for Windows, Mac OS X, and Linux systems; hit the link for instructions on using and having, well, fun in Phun.

I've been playing with Phun for a few days and have enjoyed it. If you're into physics here at the university, try it out and let me know if it's at all useful to you.