creating a game to use an entirely new Guitar controller. The concept was to have the gameplay of Amplitude with the visuals of Karaoke Revolution, both of which had been developed by Harmonix. The game was met with critical acclaim and received numerous awards for its innovative guitar peripheral and its soundtrack, which comprised 47 playable rock songs (most of which were cover versions of popular songs from artists and bands from the 1960s through modern rock). Guitar Hero has sold nearly 1.5 million copies to date. The popularity of the series increased dramatically with the release of Guitar Hero II for the PlayStation 2 in 2006. Featuring improved multiplayer gameplay, an improved note-recognizing system, and 64 songs, it became the fifth best-selling video game of 2006. The PlayStation 2 version of the game was offered both separately and in a bundle with a cherry red Gibson SG guitar controller. Guitar Hero II was later released for the Xbox 360 in April 2007 with an exclusive Gibson Explorer guitar controller and an additional 10 songs, among other features. About 3 million units of Guitar Hero II have sold on the PlayStation 2 and Xbox 360. Guitar Hero III: Legends of Rock was released in late 2007 for the PlayStation 2, PlayStation 3, Xbox 360, Wii, Microsoft Windows, and Mac OS X platforms. The title is the first installment of the series to include wireless guitars bundled with the game and also the first to release a special bundle with two guitars. The game includes Slash and Tom Morello as playable characters in addition to the existing fictional avatars; both guitarists performed motion capture to be used for their characters' animation in the game. Guitar Hero World Tour, previously named Guitar Hero IV, is the fourth full game in the series and was released on October 26, 2008 for PlayStation 2, PlayStation 3, Xbox 360, and Wii. Analysts had expected that future Guitar Hero games in 2008 would include additional instrument peripherals to compete against Rock Band; Guitar Hero World Tour was confirmed as in development following the announcement of the merger between Activision and Vivendi Games in December 2007. Activision's CEO Bobby Kotick announced on April 21, 2008 that Guitar Hero World Tour will branch out into other instruments including vocals. Guitar Hero World Tour includes drums and vocals, and can be bought packaged with a new drum set controller,