man, I want to support something like Zulip, I would even want to work on a product like this but one thing I'd say is you have to go back and study why Slack beat Hipchat and others. It's so simple in hindsight but it was the marketing and the UI/UX of Slack that made it so much easier to use. If you'd like, I have a ton of ideas and experience building UIs and would love to give you some of my input. Too much typing for a comment at the moment.
You should stop by #feedback in chat.zulip.org and share your ideas!
Regarding the history: Slack had very effective marketing, powered by a lot of venture capital. And HipChat was a weak product that had an embarrassing total hack, which did not leave customers with confidence that their data was safe there.
Zulip is not venture-funded, so we're reliant on people sharing it with others to get the word out.
As a side note, I don't think Slack could have succeeded if it launched today. Microsoft Teams has far far more users as Slack, and it's slopware. You can thank the end of anti-trust enforcement for that.
Fun fact: Shortly after MS Teams launched I created an internal "reconstituted" desktop Teams client for myself and the poor souls in my org that had MS Teams thrust upon them. It extracted resources from the (unminified!) electron app as well the js and CSS files from their web version, then repackaged it again via electron, wrapping into a standalone executable. Think like a really complicated greasemonkey/tampermonkey script.
My fork at the time replaced their criminal white space use and offered a more compact and information dense alternative using CSS and JavaScript, injected all post rendering. Ah, the silly things one is capable when faced with a minor inconvenience and a wandering mind...
