Matrix: a new specification for federated realtime chat

Matrix absolutely doesn't rely on the logically centralised ID server to function. The ID system is currently in flux (hence not being documented properly in the spec), but we've deliberately kept it layered away from the core communication layer, so that Matrix isn't dependent on it (and so we can swap it out in future). And in fact the current implementations barely use it at all, other than to *optionally* register using an email address if you so desire.

The underlying 'opaque' Matrix IDs look like @matthew:matrix.org - and like JIDs or SIP URIs are indeed DNS backed, and works just as well (or otherwise) as XMPP.

We want to do better than XMPP & SIP (& IRC) by also linking 3PIDs to theses matrix IDs - we have no expectations of foisting yet another username@domain-style namespace on the world. Whilst right now this is logically centralised (but physically decentralised, as it happens) in ID servers, the plan is to adopt a proper decentralised ID system instead - ideally someone else's, so we don't reinvent that wheel. But we haven't got to it yet :)

In terms of novel features - yes, the git-style crypto-signed distributed DAG of conversation history with eventual consistency is the main innovation (and is shamelessly lifted from Git). Decentralised ACLs are also pretty cool. Relying on 3PID mapping for identity (when it lands) will be too.

Well done for spotting the Croquet similarity - needless to say, Matrix is about more than just instant messaging, and we want it to be a general persistent JSON distributed database with EC, pubsub and strong crypto semantics. And that could be for *any* data - be it Slack-style collaboration, or whiteboarding, or indeed Croquet-style virtual worlds & cyberspace. It's called Matrix for a reason ;D