[Rochus]

This is a great sounding synthesizer; but closed-source as it seems; the compiled shared libraries can be downloaded and I found an old version of the source code here: https://github.com/bohwaz/sunvox.

[gldnspud]

The audio/synth engine source is MIT licensed as part of pixilang: https://www.warmplace.ru/soft/pixilang/

[Rochus]

Great, thanks for the hint; though the included lib_sunvox source code looks very different from the one I found on github (which is much older).