You will first need an XMPP account but then you can add GTalk users to your roster and chat with them.

GTalk has broken federation for Hangouts users, and they failed to enable s2s encryption, which is mandatory since February: https://github.com/stpeter/manifesto/blob/master/manifesto.t...

Actually we (most of the XMPP network) switched over to mandatory encryption last May and IMHO it's been pretty successful so far. Google is welcome to join the party anytime! :-)

Sounds a lot like Google's behavior on GTalk amounts to 'embrace, extend, extinguish'... except that they failed.

Can you explain, or point me to an explanation of, _in detail_, exactly what GTalk broke in terms of federation?

I find that in practice I can _sometimes_ communicate with _some_ users from _some_ clients, but it seems like it's flaky and there's not a clear pattern to it. Do you have any deeper insight?

Most of the XMPP network switched last year to REQUIRING encryption for one server to talk to another server. Google doesn't support encryption at all for server-to-server links, and thus servers like jabber.org (of which I'm the admin) can't talk to Google anymore. See more at https://github.com/stpeter/manifesto/blob/master/manifesto.t...

On Gmail, you'll need to "revert to old chat" if you've enabled the "new Hangouts".