A software modular synth that I'm building for myself, and you can use it if you want to. If you're interested, you can find some out of date documentation at https://www.reddit.com/r/BespokeSynth, or you can just jump in and start messing around.
You can find the most recent builds for Mac/Windows/Linux at https://github.com/awwbees/BespokeSynth/releases
(the current release doesn't include fubbles or most of the latest python livecoding hotness. stay tuned, I'll make a new build soon!)
Recent videos of Bespoke usage
Some context: this is my home project that I've been working on since 2011 and has grown and sprawled like weeds. It has served as a learning platform for me, which means that some of it was written by my mediocre 2011 self, some of it is written by my hopefully-less-mediocre today self, and other parts were written at various levels of my mediocrity in between. It has many modules, some of which I haven't touched in years, some of which are likely hugely broken.
These days, I only get an hour or two every few nights to work on Bespoke. It's hard to take that short amount of time and devote it to bugfixing, instead I prefer to add new features and modules. As a result, bugs can get left in the wake and some of the modules stay half-finished. Most of the bugfixing I do happens when a bug directly gets in the way of me using the software, rather than any proactive bug-chasing. I think this process is important, to keep Bespoke as my fun little zen garden, rather than a chore that I will eventually abandon.
Any releases I put up will have bugs and stability issues, but that seems better than never doing any releases at all. I can't currently see a future where a fully-stable and mostly-bug-free release would happen... maybe when I retire. Watch this space in 2050!