Flamingo is a new messenger app available for Mac OS X that combines Google Hangouts/Gtalk, Facebook Chat, and XMPP. While you can link some services like Gtalk to the native messages app itself, you don't get the gorgeous interface and experience Flamingo provides.
Once you launch Flamingo for Mac, you can start adding your accounts. Flamingo works as a system of menus that intuitively slide out only when you need them and disappear when they're not in use. The design choices made in Flamingo somewhat remind me of iOS 7 due to the flat chat bubbles and texture free interface. It's something I wish Apple had done with the Messages app in Mavericks.
If you use Facebook chat and Hangouts, Flamingo is a great way to combine the two into one app. It's worth noting that group chats aren't supported so if that's something you do often, it may not quite yet be the all-in-one solution you're looking for.
I do however find myself wishing that Apple had updated the OS X Messages app every time I switch from Flamingo back to Messages for something. It just looks better in my opinion.
If you've tried out Flamingo, let us know what you think in the comments!