Highlights include Sliding Sync (instant login/launch/sync), Native OIDC (industry-standard authentication), Native Group VoIP (end-to-end encrypted large-scale voice & video conferencing) and Faster Joins (lazy-loading room state when your server joins a room).
Their main competitor in the open-source, self-hosted space is Mattermost, which has a much more business-oriented solution, so there’s that as well.
That seems more like a direct competitor to Slack and MS Team to me rather than general communication. Matrix is a facinating protocol that keeps pushing the limits of federated communication but it always sucked as replacment for those and unless someone invests huge amounts of money in a completely new client I don’t see taht changing any time soon tbh.
And XMPP, used by the German police and NATO