While we're waiting for the Windows XP, Windows Vista and Mac versions to be available, those running Windows 7 can already take the Facebook Messenger for a spin and download the free software here.
Facebook Messenger works like the chat feature when you're logged in to Facebook. The interface is very similar to the website version with conversation tabs and navigation buttons just like how you see the social network on mobile.
There's also pop-up notifications, and News Ticker features. However, video chatting and group chat is not available.
All in all, the Facebook Messenger is an effective way to continue short-form messaging between your friends. There will be no more need to have a browser open and logged in to Facebook to get those instant messages.