This program tries to place a series of gears so that the teeth of the gears engage (but don't overlap with existing gears). The gears are different each time you run the program. This program doesn't actually simulate gears; it just lays out the gear sprites in a way that makes it look the gears are turning each other. Just click the Green Flag and watch the demo. You can also adjust the speed. Notice that if you keep increasing the speed, it creates the optical illusion of the gears going backwards. (This program isn't perfect and sometimes the teeth don't touch, but it's close enough most of the time.)
Dedicated to Seymour Papert, who seemed to like gears.