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).
technically it’s an eventually consistent federated database (or series of databases i guess? dunno), which just happens to primarily be used for instant messaging similar to discord but also inheriting features from IRC.