Frets on Fire
Frets on Fire is a game of musical skill and fast fingers. The aim of the game is to play guitar with the keyboard as accurately as possible. Only a couple of songs come with the game and many many more can be downloaded from the Song database (link below).
Frets on Fire X (FoFiX) is a fork of Frets on Fire with many new features, such as: support for 4 players, themes, bass and drum tracks.