I once wrote a game with no graphics or sound. It was a maze game: you were supposed to lead a mouse cursor through an invisible maze by touch. If you drive your cursor into a wall, it stops. You start at the bottom, and if you manage all the way to the top - you win.
Well, it's not completely useless. If you're extremely bored at work and don't want to draw attention, this could be your time waster of choice.
Explore this idea further, it would make a good tool for mental visualization and memorization as one would have to memorize and construct a mental image of the maze in order to speed up the solving, neat idea!