StepMania

StepMania is an Open Source clone of the commercial title Dance Dance Revolution (DDR).

You play the game either with a "dance mat" (using your feet) or with the keyboard (using your fingers). A song is played and arrows (up, down, left, and right) are displayed at the bottom of the screen and float upwards as the song plays. When an arrow reaches the top of the screen, you need to tap the appropriate direction either with your feet or fingers.

The arrows are played in time (and often syncopated) with the music's rhythm. They tend to hit the top of the screen "in time" with the music. When using a dance mat, you are effectively dancing to the music according to a pre-determined set of moves, however there is a lot of room for personal styles, upper body movements and and interpretive dance approaches.

There are a wide range of styles, music, difficulty settings, graphics, announcers, themes, and effects to choose from. It's possible to play multiplayer, even over the Internet.