Crayon Physics Deluxe is a cool 2D interactive game, and winner of the Seumas McNally Grand Prize at the 2008 Independent Games Festival.
Built on a Box2D Physics Engine, the game requires you to draw simple geometric shapes to solve its puzzles. The objects thus drawn, follow the basic laws of physics and shape the course of the game.
The game is a sequel to the original Crayon Physics game, which is available as a free download at the creator’s site.
Though the original game is, according to the game maker, "a quick and ugly prototype," I really had a ton of fun playing it.