There was that short period of time where most of the big players (Google, Facebook, etc.) had settled on XMPP and it was all interoperable, to some degree at least.

I even remember when Facebook first announced their support thinking "Oh sweet, now I can message all my Facebook friends from my current chat app." And when it launched, I could! But then I realized I didn't really want to.

And it wasn't long before support was dropped. I'm not sure anyone noticed.