Pop'n Music 3 Append Disc

Pop'n Music 3 Append Disc (ポップンミュージック3 アペンドディスク) is the sequel to Pop'n Music 2. It was released for the Sega Dreamcast and is designed to be used with the Pop'n Music Controller.
As the title may suggest, this version of Pop'n Music 3 is not a full game - it instead requires the user to boot up Pop'n' Music 2 and switch discs to access the extra content.