SimpleX Chat is an instant messenger that is decentralized and doesn’t depend on any unique identifiers such as phone numbers or usernames. Users of SimpleX Chat can scan a QR code or click an invite link to participate in group conversations.
-privacyguides.org
It’s clearly proving to be the most innovative technology when it comes to decentralized communication, in my opinion.
This is why I use Wire.
Desktop is a first-class app (not dependent on a mobile app), no phone number required, and syncing chats between all your devices just works.
Wire hasn’t been updated in 2 years on fdroid tho, so I’m eager to switch to something else. But nothing else exists that meets these basic usability reqs.