Most often people want to take advantage of the sweet sweet LoFi onboard synth present in the Game Boy. However this time the tables have turned and the handheld system became an integral part of a physical computing apparatus.
Jowan of file-error.net managed to interface the GameBrain cart with solenoids and play them via primitive sequencer software written in GBBasic for the GB. The project is called kBang and is worth checking out just to put a new spin on things. Thanks to Silas for sending this in.