Really nice for quick things, otherwise there is also VCV Rack (<a href="https://vcvrack.com/" rel="nofollow">https://vcvrack.com/</a>) that is a open source virtual rack with modular synthesizers. It doesn't have the graph UI that Zupiter seems to have, but a more of a skeuomorphic UI.
OP here. Feedback and questions welcome! Feel free to reply to this comment.<p>I also created a little subreddit to discuss Zupiter: <a href="https://www.reddit.com/r/musictools/" rel="nofollow">https://www.reddit.com/r/musictools/</a>
Love the simple step sequencer with scale selection. Wish this was part of a "creative scratch pad" in every DAW (It usually is possible but it's often cumbersome to set up).
I first saw one in the lovely <a href="http://www.tones.fm" rel="nofollow">http://www.tones.fm</a>