This has to be one of the coolest games to arive since Wolfenstein 3D first came out. If you were around for that, remember how revolutionary that was?
Crayon Physics Deluxe is is a 2D physics puzzle / sandbox game, in which you get to experience what it would be like if your drawings would be magically transformed into real physical objects. Solve puzzles with your artistic vision and creative use of physics.
This video says it all:
Find out more at http://www.crayonphysics.com/