Hey there,
I’m on the search for an alternative to Mattermost for a small institution I’m working with. Mattermost was the strongest contender for our needs, yet they changed their policy regarding self-hosted instances. The factor that killed it for us, is the hard cap on 250 registered users, as we potentially might need to commodate more than that.
Rocket.Chat has similar caps.
We found Zulip, and it seems as it might be what we are looking for, but we haven’t tested yet. Nonetheless, I wanted to address this community, as you may have another good idea?


Matrix (Synapse with Element) can be self-hosted for free, though they have optional paid plans for enterprises. The main goal of Matrix is federation (connecting with other servers), though this can be turned off completely. This is probably the most “business” look/feel you can get fully FOSS, if that’s what you’re looking for.
XMPP has more clients/servers, and is more for the technically oriented end user. I can’t really give recommendations here, as I haven’t extensively used XMPP.
Spacebar (formerly Fosscord) is a Discord clone (API compatibility as a goal) that can be selfhosted.
Xmpp works great for 1:1 chats and small private groups, but there isn’t really an enterprise team chat client for it. Recently some promising projects came up trying to change that, but they are still too new to be serious contenders for that usecase specifically. Maybe in 1-2 years the situation will be different.
Had to move a small team away from skype/teams quickly so renting dedicated matrix hosting in Europe and not federating the instance has been working great, except for some issues like group calls over jitsi not working properly and users reluctant to learn more odd interfaces.
Using matrix through element.io on ocassion.
It’s great.