Request for sources: Discord alternatives

I'm writing up a survey post on "chat systems you might actually want to use besides Discord", and it seems like every time I talk about this someone chirps up and asks about something new I've never heard of before. So, I want to try to head this off at the pass and collect as much as I can right off the bat. So, anyone have anything they want me to cover? Things on the list so far: Mumble Zulip Stoat Signal Matrix XMPP servers -- Prosody, Snikket XMPP clients -- Dino, conversations.im, snikket, mov.im IRCv3 Root Polyproto Spacebar Rocket.chat Mattermost Tailchat