Really nice for quick things, otherwise there is also VCV Rack (https://vcvrack.com/) 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.
However, I think Zupiter is a nice way to get people who've never played with sound synthesis interested, and the sharing feature is one thing that differentiates it from most browser-based music apps out there. You can easily show your friends what you've made, or modify what other people made.
Maybe. All but one of the modular synth guys I know are hardware purists. They look down on VCV and even semi-modular synths like the Behringer Neutron. You'd think some of these modular guys were in a cult, heh. (I've always just seen modular synths as just another tool.)