Matrix is a decentralised instant messaging platform built on the ActivityPub protocol, and thus part of the fediverse. It’s currently my default messaging app if I’m able to choose, but because of network effect that’s not a huge number of applications.
This page is my writing about Matrix.
Usernames, servers, and addresses
Modern instant messaging protcols are almost universally centralised - that is, there’s one server where everyone registers, chats, etc. Matrix, however, is decentralised but federated. That means that everyone can be on different servers, but still talk to one another.
A user’s username in matrix is: @username:server. Note the astym and colon - I will always incorrectly try to talk to username@server and @username@server because that’s just encoded in my brain.
External links
Join Matrix
Matrix outreach website
Matrix.org
Main server