Real time physics simulators

From http://users.softlab.ntua.gr/~ttsiod/games.html

I want to "lure" my nephews and nieces towards science and engineering, and one of the things I've done towards that goal is to code some real-time physics simulators.

Waves... (they look much better when they move :-)

All the code I wrote is available below, and compiles under Linux, Free/Net/OpenBSD, Mac OS/x and Windows (with GCC/MinGW), with the usual...