I get the sense that Mattermost is the same kind of eventually-get-you-paying play as Slack.
Other threads are mentioning Zulip, which feels more old-school free as well as Free open source.
Other threads are mentioning Zulip, which feels more old-school free as well as Free open source.
Open standards, easy migration, and servers you pay an honest cost for. Self-hosting, perhaps even. That's where we need to go.