[croon]

I wasn't a pro about it, but I set up and ran our XMPP at a previous company. What I saw as a real problem was a split between clients, servers, modules over the protocol, so it definitely wasn't painless in what functionality worked between one server, modules, a client and inevitably someone choosing a different client. You might do it better than me and it ends up working great for you, or it's gotten better in the last few years since I tried it, but if my experiences are any indication I wouldn't recommend that route. YMMV.

But if you don't like Slack, I'm guessing Mattermost is out of the question as well. I'm still using IRC in a lot of places which "just works", but obviously that is missing a lot of features and fluff of newer technologies, even if some can be retrofitted in.

Please et me know what you decide and your success since it's still relevant for me in a couple of places.