The User Writable Quantizer looks pretty interesting and I may have to build it someday. But neither of these does quite what I really would like in a quantizer (multiple stored microtonal scales and easy reprogrammability), nor do any other DIY quantizers I know of, so I’m considering designing my own.
@Dud I just built this Barton User Quantizer PCB and am making it into Kosmo format right now. I know it’s not Arduino based, but you can build your own scales, which is why I liked it and an easy build.