Just from my head:
IRC, XMPP, Matrix,
SMS, RCS,
Session, SimpleX, Nostr, Jami, Tox, OnionShare, DeltaChat, Sup., GNUNet Messenger, Mumble, Zulip, Briar,
Signal, Wire, Threema,
Snapchat, Telegram, Facebook, Facebook, Facebook, Discord, Slack, iMessage, Google Chat, Twitter, KakaoTalk, WeChat, GG, TeamSpeak.
This post is not for discusson which one of standards, networks, services or garbage is the best for anything. This is a call can we just stop making more?
We basically only have fully functional email because big tech wasn’t around yet to control it. We’d probably have umpteenth different versions by now if that wasn’t the case, none of which could talk to each other.