Trillian for Mac is a free messenger that makes it easy to chat with your friends no matter where they are. Use Trillian to connect to Facebook, Windows Live, Twitter, GTalk, AIM, Yahoo, and much more. As an added bonus, Trillian for Mac syncs beautifully with Trillian for iPhone when you're on the go!
Popular and, probably, the best instant messaging client for you Mac.
Freeware Mac OS X IRC client created by Steve Green.
Instant access to multiple Facebook accounts and desktop notifications.
Use Facebook Messenger right from your macOS desktop.