why not mattermost which is open source you can selfhost and is really really good.
didn't mattermost recently make some changes to their license that put a bunch of features behind a paywall?
https://news.ycombinator.com/item?id=46383675
didn't mattermost recently make some changes to their license that put a bunch of features behind a paywall?
https://news.ycombinator.com/item?id=46383675