I stumbled across this Flash game called Magic Pen in which your goal is to move a red shape to a goal area by drawing little shapes and letting physics take place.
The game rule are extremely simple: you can draw shapes and attach them to each other with rigid (mostly) joints or hinges that allow the piece to swivel about each other. You can either draw polygons or you can draw rolling circle objects.
The drawing detection of the polygons is not too bad, but a little flaky sometimes. It's good enough that the game is quite fun because you eventually have to start building up lever systems with counterweights and stuff to move the red shape to the goal area. Occasionally, I found myself drawing shapes and dropping them on objects in motion to adjust the movement of the object.
The game is definitely worth a few minutes (or hours) of enjoyment. I love these more unusual games.