Facebook Messenger 1.2.205.0 For PC

Facebook Messenger is an instant messaging service and software application which provides text and voice communication. Integrated with Facebook's web-based Chat feature and built on the open-source MQTT protocol, Messenger lets Facebook users chat with friends both on mobile and on the main website.

Messenger for Desktop

Messenger for Windows Desktop was "officially" released on March 5, 2012 for Windows 7 users.
Testing on the software began among a limited beta tester group on November 21, 2011; however, a leaked link to the beta-stage software was publicly revealed to tech bloggers by Israeli blog TechIT. Facebook responded the same day by announcing the link's availability through its Help Center.
Among its features is a "ticker" similar in function to the sidebar of friend activity seen by Facebook website users. At the time of release, "chatting with multiple friends, video calling, limiting chat availability and editing settings" were not available through the software. A Mac OS X version was mentioned by Facebook developers as forthcoming.