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?
All these tools serve a slightly different purpose, for a slightly different group of people. In China, not using WeChat is impossible due to the way it’s integrated everywhere. Slack is more suited for development/work channels, Discord is more suited for gaming. If there are enough people that could say “None of these satisfy us, we want a different alternative to communicate”, that’s good grounds to build it in the first place.