You knew it was only a matter of time before Flash was used for pure evil. John Tantalo, who could be using his talents to cure cancer or something, has written the Planarity Flash Game. The game generates random planar graphs and draws them to hide the fact that they are planar. You the player (or rather victim) must move the vertices around to show that it really is planar. The game is hard, but moving the little dots around is incredibly hypnotizing.
Via Eszter at Crooked Timber.