You can download Messenger App for Windows 7 from this site: Messenger App Download [1] . Currently, Windows (installation and portable version), Linux (Ubuntu/Debian and Fedora RPM), Mac OS, Android, iOS, Windows Phone are all supported. read more
However, there is a bit variation that you will experience with every other OS; but, all of them are officially developed by the Facebook Inc. Must Read: Download Facetime for PC Free (Windows 7/8) Facebook Messenger was initially rolled out as messenger application for Android and iOS, in August 2011. read more