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).
I’m not the best person to ask as I just chat on a few channels in a single server.
There definitely are software projects that run their real-time support through Matrix in the same way others do it through IRC or Discord.
At the same time most servers seem to have a General room (or similar) for off-topic chats.
Peruse the big list of public rooms here. That might give you a sense of it.