Mutable Instruments is all about open source, it’s all in their Github repositories, but all their schematics and PC board layout files are in EAGLE’s older binary format which KiCad cannot import. I decided open source is pretty much bullshit if you can’t look at the files without a subscription to software you otherwise don’t even want. (And I certainly don’t otherwise want Fusion 360, which is now the only way to get EAGLE. There isn’t a Linux version, so I have it on my old Mac, where it runs like a constipated hippopotamus. Ugh. You can get Fusion 360 for free, but for only one year; after that it’s $100 a year.) So:
I made forks of several of the Mutable Instrument repositories:
For all but the first of these, the forked repositories are identical to the original except that I read all the .brd and .sch files into Fusion 360 and then exported them in EAGLE XML format. So they now can be imported by KiCad. And I added a sentence saying so to the README file. For the breadboard-friends repository I did that, but also added a folder containing KiCad versions of the projects, and I added a KiCad-only adaptation of bbf-eurojacks for Thonkiconn jacks.
Mutable has a bunch of other repositories but these looked like the five of most interest to me. If you’re a KiCad user, have a look.