Astro Messenger!

Facebook Messenger is a faster way to message. Reach friends right on their phones, get and send messages fast, message everyone at once and more.

Adium is a free and open source instant messaging application for Mac OS X, written using Mac OS Xs Cocoa API, released under the GNU GPL and developed by the Adium team. Based on the libpurple protocol library, Adium can connect you to any number of messaging accounts on any combination of supported messaging services and then chat with other people using those services.

Digsby is a multiprotocol IM client that lets you chat with all your friends on AIM, MSN, Yahoo, ICQ, Google Talk, and Jabber with one simple to manage buddy list. Its also a social networking tool that alerts you of events like new messages and gives you a live Newsfeed of what your friends are up to on Facebook, Twitter, MySpace and more.

Private instant messaging via secure, distributed technology.

Pinger lets you text and talk free with the people you care about most, anywhere on the planet. Tap a picture and you'll see all of your communications—texts, pics, calls, voicemails—all in one place.

If you don't want to get distracted by Facebook, or throw away your privacy with the mobile messenger app, but still need to chat, try deface.

Facebook Chat IM is a Desktop Messenger for Facebook. With it you can chat with all your Facebook friends directly from your Desktop. It has a simple and easy to use interface and offers many great features such as emoticon, status update notification, sound alerts, chat history and much more. It’s written in Java and released under the GNU LGPL.

Gaption is a platform that empowers people to pursue what they love doing, by allowing them to monetize their passions, skills, and content through a fun and delightful experience.

Unofficial Facebook Messenger app.