Zyn-Fusion is a new user interface for ZynAddSubFX, one of the most
popular open source synthesizer. As far as I understand, it is meant to
replace the old user interface.

homepage: http://zynaddsubfx.sourceforge.net/
sources: https://github.com/mruby-zest/mruby-zest and
https://github.com/zynaddsubfx

Regards,
Yvan