what chat program?

What chat program should I be using these days to ensure maximum cross-compatibility? I suspect there isn't an answer. It used to be that I would use a jabber based chat client and I could talk to google (xmpp), msn (via a bridge), and anyone else running XMPP based services. Then MSN went to something incompatible and stupid (Skype?), and now google have gone to hangouts which is not XMPP, and I'm left with connectivity to the remaining few people still using the old google chat client. Frustrated. James