An interesting web/node based collaborative, interactive, graphical, generative/procedural soundscape engine. It would seem to tick a few boxes for Zynthian given its cross platform, operates as a server and has a web interface. Not that I know much about integration but it looks like it has the right sort of connections like for JACK and midi/osc.
Fragment is a collaborative cross-platform audiovisual live coding environment with pixels based real-time image-synth approach to sound synthesis , the sound synthesis is powered by pixels data produced on the graphics card by live GLSL code, everything is based on pixels!
Fragment is able to produce high-quality fast additive and granular synthesis simultaneously with re-synthesis support , subtractive and PM synthesis is also supported, it has many features making it a bliss to produce any kind of sounds or visuals and is aimed at artists seeking a creative environment with few limitations to experiment with, a programmable noise-of-all-kinds software / sound design tool.
Many videos of most features are available on the official YouTube channel
An intro tutorial and a working demo app I made from the tutorial code. Press the pause button to play a 440hz tone.