This program is customised geometry built from Squeak (formerly Smalltalk). I'm finding that it's great fun to play with. It's available on Linux, Windows or Mac as well as the OLPC. Hilaire Fernandes, the developer, has created over 60 short screencasts, in ogg format, which provides a great way to learn the program.
Above are some screenshots from an exercise I learnt from viewing the 305-rotation-geometric-angle-degree screencast. Create an angle and then dynamically vary the angle - nice! Rotate a polygon around a point and then vary the angle of rotation. This one is a lot of fun!