This virtual modular synth is amazing... there are seemingly infinite possibilities. And better yet... IT'S free!!! I would rate this 5 stars, however it crashes pretty much every other time I use it, and when using big modules I experience lag. It is possible to ignore the lagging, however the crashes can become annoying. Despite this, I am soooo thankful to the creator of this software for making it. It is one of my favourite audio applications.
Although I don't own any Eurorack hardware I've seen videos of this thing being compared to it and I can't tell the difference. The latest version will connect to your DAW (though not quite a full-fledged plugin). I think this is pretty amazing software, AND it's free and open-source.