I just lived Politehub, it could be an alternative for Slack, kindly give it a try, guys!

Thinking about the same. Anyone experiences with Zulip vs Matrix/Element? Both seem to be the only true and mature foss solutions Dabbled with both a bit and so far felt that Zulip is a bit more polished and communication friendly. Use case is for a small startup (around 10 people and growing). Thoughts?

We've got a license for Teams that we don't use.

Mattermost.