Matrix: a new specification for federated realtime chat

From my perspective, XMPP is all about message passing, whereas Matrix is all about state synchronisation (yes, I know they're two sides of the same coin, but they are opposite ways of addressing a similar problem). Matrix is basically an global EC DB with open federation and pubsub. A good analogy is that XMPP is like SMTP (with some storage extensions like IMAP), whilst Matrix is like NNTP. It's worth noting that XMPP does have some extensions like Buddycloud and FMUC which do provide decentralised persistent messaging - but with Matrix we wanted to see what'd happen if we just built on plain HTTP/JSON rather than the XMPP stack.