Guitar Hero World Tour is the fourth major release in the Guitar Hero series of music video games, a series that has sold over 24 million units and earned more than $1.6 billion in retail sales.[1][2] The game was released in October 2008 for the PlayStation 2, PlayStation 3, Wii, and Xbox 360 game consoles in North America, and a month later for PAL regions. It was released in Europe and on a limited basis in North America for the Microsoft Windows and Apple Macintosh platforms.[3][4] The game was developed by Neversoft, with assistance from Vicarious Visions and Budcat Creations for the Wii and PlayStation 2 versions, respectively, and distributed by RedOctane and Activision. Guitar Hero World Tour, like the other games in the Guitar Hero series, focuses on the use of special game controllers to mimic musical tracks from popular rock songs that date from the 1960s to contemporary hits. While previous versions of the series have only used a guitar-based controller for lead and bass guitar tracks, World Tour adds in drums and vocals, allowing up to four players to create a virtual band. For each instrument, the player scores points by matching controller actions with note gems on the game screen to avoid a bad performance that may end the song prematurely. In addition to the on-disk songs, the PlayStation 3, Xbox 360, and Wii versions support the ability to obtain new songs through downloadable content. A new music creation system also allows users on the same systems to gain new user-created songs through the game's "GHTunes" service.