The Messenger for Desktop is a desktop client for Facebook's instant messaging service that lets you access it if you do not open a full social network in your browser - with the benefits that come with it. (Some reactions, for one!)
This unauthorized client is based on the web service offered at Messenger.com, which allows you to access all features without any limitation. With it you can chat with your contacts and groups; Send photos, videos and stickers; And make phone or video calls. In addition to everything, it also supports desktop notifications, so even though the application is low, you will see an upcoming chat notification.
Obviously you need a Facebook account to use it. This lets you synchronize all your activities on the rest of the client on other platforms, whether it is the website or the chat feature of various Facebook smartphone apps.