StepMania is a rhythm game for Windows, Mac, and Linux. It features 3D graphics, keyboard and "dance pad" support, and an editor for creating your own steps.
Arrows scroll up from the bottom of the screen and you must hit a button in time to the music. Also, you will hit a different button depending on which direction the arrow is pointing. The game can be played with your hands using the keyboard, but the real fun comes when using a "dance pad" with foot sensors.