Freeware - DISTRHO Cardinal Virtual Modular Synthersizer VSTi Plugin

https://github.com/DISTRHO/Cardinal

Cardinal is a free and open-source virtual modular synthesizer plugin, available as JACK standalone and AU, LV2, VST2 and VST3 audio plugin for FreeBSD, Linux, macOS and Windows. It is based on the popular VCV Rack but with a focus on being a fully self-contained plugin version.