i just saw this project on google code
a 4 bit MIDI synth based on the Atmel AVR ATMega48
it looks kind of cool, figured i would share.
here is the makers description
"4bitsynth is a MIDI-controlled digital synthesizer that uses the Atmel AVR ATMega48. Inspired by the NES, the sound is 4-bit. The digital output is put through an R-2R resistor ladder to get the analog waveform."