Games which include music-generated content have music that is directly influential to the gameplay. Music will spawn enemies, create obstacles, and have a variety of other effects on the game. Note that this does not include games where the music is influenced by the game (i.e. Bit.Trip Beat, Groov, Fractal), but is limited to games that are influenced by the music. Typically, games that include music-generated content allow users to either play a default set of songs or use their own songs.
An earlier example of music-generated content, Vib-Ribbon is a 1999 PlayStation titled developed by famed game designer Masaya Matsuura (also known for PaRappa the Rapper). In Vib-Ribbon, players control a wireframe character who navigates procedurally generated levels based on either a CD that the player has put into the disc tray or preselected songs. Vib-Ribbon produced two sequels, both on the PlayStation 2: Mojib Ribbon (which was based more around rap music) and Vib Ripple (which instead of being focused around music, was focused around the importation of photography).
The Monster Rancher series has a unique take on music-generated content. Most of the games in the franchise have given players the ability to import their own music, which is then used to create a monster. The original Monster Rancher supported music CDs in the PlayStation's disc tray, while future incarnations have offered different ways to import music. For example, Monster Rancher DS allows players to create monsters by speaking into the microphone (or playing sound into the microphone).
One of the more popular examples of the implementation of music-generated content, Audiosurf allows players to import their own songs, at which point the game will create a track for the player to fly on. As the player progresses through this track (as well as the song), there are blocks that have been created at certain points. Picking up these blocks to match them, while avoiding other blocks, is key to scoring high. Picking up three blocks of the same color in a row makes them disappear and earns the player additional points.
Beat Hazard is a twin-stick shooter, akin to Geometry Wars: Retro Evolved, with one key difference. Uploaded music determines the frequency at which and what type of enemies are spawned. Initially released on the Xbox Live Indie Game marketplace, Beat Hazard was later released on Steam and the PlayStation Network. Players are able to upload any music compatible with the respective systems, although on Steam an additional piece of downloadable content is required to import music from iTunes.
A relatively recent release, The Polynomial is another shooter that utilizes music-generated content. Available on Steam for both Mac and PC, The Polynomial is a three-dimensional space shooter, where the music generates a wide variety of fractals and abstract shapes. The player is able to either explore these worlds in free play, or attempt to stay alive for certain amounts of time, scoring as high as possible.