I can’t remember if I’ve mentioned this around here, but I can’t recommend Crayon Physics enough. It’s a blast to play, and there’s a free demo here if you want to tinker:
A quick search for videos turned up this little gem:
It’s a great diversion from the MMO grind that has a nasty tendency to cause ennui. Plus, kids like the game. That’s always a plus.
(Oh, and it’s somewhat similar to Line Rider, another fun little physics toy. Can you tell I was an Etch-A-Sketch/doodle in the margins sort of kid?)