IMHO Zulip is a great choice for text chat for teams for companies. In your case take a look at Movim, XMPP based, Movim can do blogs and more: https://movim.eu/

I manage a self-hosted Zulip instance on a VPS and have been quite impressed overall. The install/updates/maintenance have all gone very smoothly with no real problems over several years across major versions.

When evaluating options, Zulip won because of its unique “topics” feature that helps organize conversations in channels so they are not so fragmented and difficult to follow/find later. It may take some users a little bit to get used to this but it’s worth it IMO. Or you can choose to not use topics and it’s still a good choice for chat with permanent searchable history.

Best to try it out and see how you like it, the install is very painless.

I hate the UI, it looks/feels too much like Slack

Zulip pretty easy to self host. I ran a server for a group of friends a little while back, and it worked great. The UI takes a bit of getting used to, but it is great once you do because everything is a thread by default. And that makes it really easy to catch up on things.

It's quite good from my experience, better than Matrix for group based communication thanks to the threads structure (supported everywhere as opposed to Matrix where even Element X don't support them officially). It's not federated, but for your use case it shouldn't be too much of an issue.

took one look, said needs an external video/voice provider (e.g. zoom, jitsi,...), said bye.

It's good. Used it for some NixOS governance stuff. It feels like a hybrid between chat and forum, so it's good when you want to have semi-structured discussion but still want to stay on top of all topics.

What are you using for voice chat? As far as I know neither Zulip nor Foundry have native voice chat support.

For D&D we usually find it more convenient to keep our notes inside of foundry. I feel like foundry+Zulip+some CMS+some voice chat might be a bit tedious.

Is there a particular reason for Zulip vs something like Signal or Jitsi or Matrix? (Also asking for myself because I've been looking into Matrix again lately and this is the second time I've seen Zulip come up and in relation to VTTs lol)

Why consider it? Just give it a try.

I don't necessarily have any objections other than the navigation is just horrendous. You don't have a traditional channel, every single message has to go into a thread.