This is a two guys, one synth demo of what could be the ultimate Commodore 64 synthesizer, a C64 customized to work with Cynthcart.

via kilobyte242:

fully customized Commodore 64, enhanced for Cynthcart. Features SID2SID installation, Linear/Slider pot for Cynthcart filter, active guitar effects (overdrive and frequency filter) for each SID’s output, an mounted musical overlay, feedback knobs…..for more information check out www.kilobytemodshop.com