This innovative Swedish engineer converted an old electric organ into an 8-bit synthesizer which can play fantastic renditions of your favorite NES theme songs. For modern 8-bit music, check out this collection.
With all the original tone generating parts removed, the keys, pedals, knobs and switches have been rewired to a microcontroller which converts them into MIDI signals. Those are then picked up by a second microcontroller, which acts as a synthesizer. Check out the build details for more info.