VCV Rack

Andrew Belt released Rack as open source in 2017. Modules sit in a rack and are patched with cables carrying simulated control voltage and audio, following the same voltage conventions as the hardware format. The library quickly grew to thousands of modules, many free, several of them faithful ports of real modules whose firmware was already open.

Rack 2 arrived in 2021 with a paid Pro edition that runs as a plug-in inside a DAW; the free edition is standalone. It became the cheap way to find out whether modular synthesis is for you before bolting expensive modules into a case — and, for many people, the replacement for doing so.