StarLogo/OpenStarLogo

Turtle Geometry (see Mindstorms: Children, Computers, and Powerful Ideas) started out at MIT's AI Lab way back in 1970. If you've seen or heard of LEGO Mindstorms NXT, you'll find that many of the concepts it embedded into this robotics kit came from Seymour Papert's Mindstorms book and Turtle Geometry.

StarLogo and OpenStarLogo lets you (or your kids) learn about Turtle Geometry and the Logo programming language on computer running Microsoft Windows, Mac OS X, or UNIX/Linux.