With SaaS like slack and popular open source options like Mattermost and Rocket Chat, I don’t expect the Zulip node to be particularly popular.
However I still wanted to write and express my appreciation for including it, as it is very useful and works flawlessly (as does Zulip itself).
I honestly think more people should take a look at Zulip who already use chat apps like slack, because whilst Zulip may not have the direct integrations, when using n8n it obviously has all the integrations n8n provides, it’s also self-hosted so no pay-per user fees! We run 50 users for $10/m, thats $250 if you run on Slack 
So thanks n8n for including these fantastic open source projects in yours!