Stay away from proprietary crap like Discord, Slack, WhatsApp and Facebook Messenger. There are enough FOSS alternatives out there:

• You just want to message a friend/family member?
  • Signal is the way to go
• You need strong privacy/security/anonymity?
  • SimpleX
  • Session
  • Briar
  • I can't really tell you which one is the best, since I never used any of these (except for Session) for an extended period of time. Briar seems to be the best for anonymity, because it routes everything through the Tor network. SimpleX allows you to host your own node, which is pretty cool.
• You want to host an online chatroom/community?
  • Matrix (Element)
  • Revolt
  • (XMPP)
  • (IRC)
• You need to message your team at work?
  • Mattermost
  • Rocket.Chat
  • Zulip
• You want a Zoom alternative?
  • Jitsi Meet