VCV Rack is a titan in the FOSS eurorack modular world. nothing else comes close. I have a physical eurorack as well but i use Rack all the time to sketch out ideas and to explore new kinds of modules before i buy something physical.

See also LV2/JACK CV: https://linuxmusicians.com/viewtopic.php?f=1&t=20701

Sadly running it as a DAW won't be open source.

Though running the FOSS version on linux allows to route audio back and forth between Rack and external recorders, hosts, plugins, etc with ease via JACK.