Guitar Hero is a series of music rhythm game video games first released in 2005, in which players use a guitar-shaped game controller to simulate playing primarily lead, bass, and rhythm guitar across numerous songs. Players match notes that scroll on-screen to colored fret buttons on the controller, strumming the controller in time to the music in order to score points, and keep the virtual audience excited. The games attempt to mimic many features of playing a real guitar, including the use of fast-fingering hammer-ons and pull-offs and the use of the whammy bar to alter the pitch of notes. Most games support single player modes, typically a Career mode to play through all the songs in the game, as well as competitive and cooperative multiplayer modes. With the introduction of Guitar Hero World Tour in 2008, the game includes support for a four-player band including vocals and drums. The series initially used mostly cover versions of songs created by WaveGroup Sound, but most recent titles feature soundtracks that are fully master recordings, and in some cases, special re-recordings, of the songs. Later titles in the series feature support for downloadable content in the form of new songs. In 2005, RedOctane, a company specializing in the manufacture of unique game controllers, was inspired to create Guitar Hero based on its experience creating hardware for Konami's Guitar Freaks arcade game. It enlisted Harmonix, which had previously developed several music video games, for development assistance. The first game in the series was made on a budget of US$1 million. The series became extremely successful, leading to the acquisition of RedOctane by Activision in 2007. Harmonix was acquired by MTV Games and went on to create the Rock Band series of music games in the same vein as Guitar Hero. Activision brought Neversoft (primarily known for their Tony Hawk series of skateboarding games) on board for future development duties. Additional companies, such as Budcat Creations and Vicarious Visions, have assisted in the adaptation of the games for other systems. The series has twenty-five releases, including the two spin-offs, the DJ Hero series and Band Hero. The Guitar Hero franchise was a primary brand during the emergence of the popularity of rhythm games as a cultural phenomenon in North America. Such games have been utilized as a learning and development tool for medical purposes. The first game in the series was considered by several journalists to be one of the most influential video games of the first decade of the 21st century. The series has sold more than 25 million units worldwide, earning US$2 billion at retail. Despite early success, the series, along with the overall rhythm game genre, suffered from poor sales starting in 2009. Despite asserting consumer research suggested continued solid demand for the series, Activision later stated that the series was on hiatus for 2011, amid the development of a seventh main installment that was later cancelled as the emerging product was considered to be of poor quality. Activision later shut down sales of the series' downloadable content, although users who purchased material from it previously may still play what they bought. Guitar Hero Live, released in October 2015, was the first new title in the series in five years, considered to be a reboot of the series and developed by FreeStyleGames, which had developed the DJ Hero games. Following a lukewarm reception and sales, Activision laid off many of the game's developers and sold the studio to Ubisoft, later shutting down the game's streaming DLC service.