Love this.
There's a sense in which this isn't the most practical choice -- general purpose synths (software or hardware) and libraries available for most runtimes give you all the power you need to create the bleeps and bloops.
But there's also something good about old things and limited things being put to good use, and finding ways for creativity to thrive in constraints.
Nice, but without any "sync" capabilities unfortunately useless in a multi-instrument context.
For the record, the word "qotile" in the domain name is from the game Yars Revenge, one of the most fun (imo) games for the 2600:
His Cynthcart for the C64 is much better and more versatile, I use it often with a midi keyboard to make chiptunes.
There is also the Mssiah cartridge, it even has a MIDI IN. Totally sick cartdrige. I integrated my C64 into my multi-instrumental MIDI setup driven by Cubase on an Atari ST with this. :-)