Hardware in 2010
The Fluxamasynth is a full fledged synthesizer on an Arduino shield. 16 channels, 64 voice polyphony provided by an Atmel ATSAM2195. An Arduino library of convenience functions makes it easy to control pitch, chorus, reverb and the built-in equalizer. See the Modern Device website for more details.
Here it is with an air pressure sensor:
The shield has a 3×7 header on the analog pins that allow the use of servo cables to remotely wire sensors or pots:
Here are some earlier revisions:
And the schematics: