Linus Akesson’s Chipophone is a homemade 8-bit synthesizer, designed for live chiptune playing.
It has been built inside an old electronic organ. All the original tone-generating parts have been disconnected, and the keys, pedals, knobs and switches rerouted to a microcontroller which transforms them into MIDI signals. Those are then parsed by a second microcontroller, which acts as a synthesizer.
Details at the Linusakkeson site.