Guitar Hero World Tour’s song-sharing service was GHTunes.
World Tour introduced Music Studio, allowing players to compose custom tracks either note by note or in real time. Those creations could then be uploaded and accessed by other players through GHTunes, using the online features of the Xbox 360, PlayStation 3, and Wii versions.
GHTunes was not the name of the creation tool itself. Music Studio was where songs were made; GHTunes was the service associated with finding and sharing user-created music. That distinction is the main source of confusion in this question.
World Tour was also notable for expanding Guitar Hero beyond guitar-only play. It added drums and vocals, supported four-player bands, and shipped with 86 licensed master recordings. Its custom-song system made the game feel more like a small community music platform than a fixed soundtrack game.