It's 'extensible.' That's what they say. 'Extensible.' You know what that means? It means they didn't finish it! It's like buying a car, and they say, 'Oh, the engine? That's... extensible. You figure it out!'

We had XMPP in facebook's messenger and google talk up until both companies decided that they embraced this open protocol enough and removed support /s

Pretty sure someone recently commented on XMPP and why it failed - mostly because of variety of servers and clients which differ among each other too much.

In Poland the second most popular instant messenger network during the "golden period" beside Gadu Gadu was Tlen.pl. It used a modified XMPP but it was never fully compatible with it - it was impossible to reach contacts from tlen.pl domain. Then facebook arrived and people moved from "domestic" networks to global ones.