I have been using Rocketchat for some long while at work.
I had a test instance that I have converted over to use by a few of us to discuss bugs & releases & stuff.
If anyone is interested in chatting then let me know and I can potentially add you in.
Currently I only run LDAP Authent so have to manually add users.
It is possible to use generic registrations, and even OAuth with the likes of github, FeckBook, Gobble etc etc
I have only been doing this for a bit of fun and to make my life easier.
If anyone wants to chat then let me know and I will set up a general chat channel.
For the technical, Rocket runs on Docker on SME v9 on a VM on Proxmox on a server somewhere in France
It IS a test machine for my work install so it is a bit underpowered and may be flaky, but if enough are interested then I may look at something a bit more heavy duty.
Anyways, let me know if you want an account.