Iain Sharp built a single-board, open source modular synth packing some pretty cool features:
The LushOne kit is designed to provide the core functions of a modular synthesizer in a low-cost single board design. The LushOne can be controlled from a MIDI keyboard or PC interface to allow you to play the instrument with equipment you already have. The LushOne can be interfaced to analog control voltages to allow you to play using alternative controllers like joysticks, optical or distance sensors. The signal paths between modules are routed with patch leads so you can combine the modules in different ways to create new effects or you can interconnect the LushOne with other external modules.
Iain is selling a kit and they cost 69 pounds.