Remember Facebook's Chat Head feature? When enabled, small circles containing the avatars of your contacts would show up on the screen of your Android device atop all other windows. (iOS users were able to use the feature for some time, but the Messages transition put an end to that.)
The feature made it possible to continue a conversation without having to leave the app you're using.
As The Next Web pointed out today, there's a free app in the Mac App Store that brings the same Facebook Chat Heads functionality to your OS X device.
Appropriately called Chat Heads, the free app connects to your Facebook account and places the same avatar circles on your desktop. You can then start new conversations, carry on old ones, and use Facebook's chat feature just as you'd expect.
Through in-app purchases you can unlock new themes, a menu bar icon and new message alerts. However, as of right now, all in-app purchases are free. Double win.