XMPP in the browser
XMPP is a very mature and robust communication technology. But unfortunately, it hasn't seen broad adoption in the web community. It's quite possible to use XMPP directly in the browser and we've done so extensively. We've built chat dashboard systems and a live mapped asset tracking system for RECON Dynamics, both using XMPP.
This can be used for lots of interesting things, for example federated WebRTC calls over XMPP.