Facebook app for OS X
Windows has a Facebook Messenger app that you can grab through the Windows Store (which apparently isn’t very good). Apple fans, however, have no official option from Facebook that they can use—not yet, at least.
Facebook is working on messenger app.
You’re probably wondering why this even matters, especially if you’re one of the many, many people who use Facebook the conventional way: You open a Web browser, you browse around the site, and you chat with your friends using its built-in messaging features. Easy as that. If you’re especially crafty, you might even just use good old messenger.com if you want to be able to chat with your friends without being tempted by any of Facebook’s other distractions.