You know Line Rider, right? You don't! It's the Flash game where you draw a track for a little guy on a sled, who through the power of gravity and physics will swoop along your creation. Build things carfully and he'll have a lovely ride. Mess up, and he's go splat head-first into the ground, fly off his sled, and there will be sad faces all round.
Thing is, if you've had a go, you've probably discovered how tricky it is to be elaborate. In which case, this should make you cry: