XMPP is one of those things that billions of people use without knowing it. Facebook Chat and GChat for a long time (and maybe still now) were actually just bra

XMPP is one of those things that billions of people use without knowing it. Facebook Chat and GChat for a long time (and maybe still now) were actually just branded XMPP solutions - Facebook (annoyingly) shut off federation, keeping in the spirit of their walled garden approach, but GChat still interoperates with other XMPP servers if I'm not mistaken. Edit: GTalk shut off federation for XMPP extensions like multi-user chat and Jingle (Voice-Over-IP). As for IRC - yes it has been largely eclipsed by proprietary solutions. I chalk this up to the lack of a compelling, truly simple web front-end for it. For instance, Slack seems to imitate a lot of the feature of IRC - it would be easy enough for it to just be IRC underneath, and maybe it is. But as far as I know nobody ever wrote a true web client for IRC that was compelling enough for the mainstream.