Slightly off topic: There is the Lira-8 viewtopic.php?p=164557#p164557 and as a mod plugin the Cosmic viewtopic.php?p=164559#p164559. (The Soma Simplexfm (HW) manual says at the end:
And finally, SimplexFM demonstrates the capabilities of the Metaconformer module itself,
which is a completely open system. Its hardware and CPU completely belong to the user.
If you know how to program in C, then welcome. Write your own synth and share it with
the world!
If you don't know how to program in C, but want to learn how to program for hardware,
then Metaconformer will be an excellent starting point for you in this path. All the hardware
is already assembled, you just need to learn how to write software.
Start from flashing LEDs, through your own MIDI controller, to a custom polyphonic synth.
.)