A free virtual modular synth application. It's mad crashy on my pc but it's still cool and a work in progress. I always wanted to try out some synths like this. Apparently some of these VCV rack modules are made by hardware synth creators and the vcv versions run exactly the same software. Bit of a learning curve though. All I've done so far is lose hours to creating the kind of droney bleep soundscapes that I dislike.
VCV Rack - Open-source virtual modular synthesizer
VCV Rack - Open-source virtual modular synthesizer