Facebook Messenger was originally developed by Facebook, Inc. as Facebook Chat in 2008. In April 2014, Facebook announced that the messaging feature would be removed from the main Facebook app and users will be required to download the separate Messenger app.

Messenger is an instant, free messaging feature that connects to the Facebook database and has replaced the in-app Facebook messaging service. It allows Facebook users to connect with each other and send instant messages, emoji, photos, videos, and perform other light tasks.

After being separated from the main Facebook app, Messenger hit 1.2 billion users in 2017.

The app allows its users to send messages and exchange photos, videos, stickers, audio, and files, as well as react to other users' messages and interact with bots It also supports voice and video calling. The standalone apps support using multiple accounts, conversations with optional end-to-end encryption, and playing games.

You can use Messenger on their official webpage or download the app from the App Store or Google Play.