Earlier quoted context omitted.
Tell me more about Zulip?
It's everything you want in a threaded chat server except federation. Web client is responsive and has good shortcuts. Easy-ish to self-host, cheap to buy hosted. Configurable privacy. Integration with all sorts of stuff, including email. A little lacking in community moderation tools. Text-mode client works acceptably well over a low-ish bandwidth connection. IOS and Android clients. Open source.
We had an IRC server. IT and Ops used it.
We moved to ejabberd. IT, Ops, and a couple of devs used it. Not all.
We moved to Zulip. Everyone in the company uses it.