Guitar Hero: On Tour
Guitar Hero: On Tour is a music video game developed by Vicarious Visions and published by RedOctane and Activision. It's the first Guitar Hero game made for a handheld game system.  To play, players use Slot 2 (the bottom loading slot of the DS) to attach a device with red, green, blue, and yellow buttons on it.  The player uses those four keys to play the game.