There are quite a few software versions of Mutable modules in the interesting new open-source, cross-platform VCV Rack software modular synth system:
I’ve not had time to test it properly yet, but after a 5 minute play it seems quite good, and far from a toy (the topic was just clickbait). And it has a well-defined plug-in architecture, and it’s all completely hackable.
It should pair nicely with an Expert Sleepers ES-8 (and ES-3) for high quality, DC-coupled and audio bidirectional interfacing with physical modules. And it may even run OK on an RPi3b with a 800x400 pixel touch screen display, which fits nicely between euro rack rails - that is yet to be tested.
I was never very fond of the zMors software modular, although the Audulus software modular synth system is excellent, but a bit more low-level, and a bit tedious to use and build higher-level modules with. This, however, seems just right, and it’s open-source. Nice!