Palringo for Mac

Palringo for mac is a mac freeware that use a wide assortment of messaging options when talking to those they know online. With this app you can send text, voice, or photo messages. You can update your social network profiles as well. It supports Facebook, Windows Messenger, AOL, Google Talk, and more.

Camfrog

Video chat 1-on-1 and join video chat rooms. No webcam is required to see people. Camfrog works behind all firewalls, routers, and wireless networks. It’s easy to find new people to video chat with our user directory.

Adium

A free instant messaging app that can connect to AIM, MSN, Jabber, Yahoo, and more. Under active development and highly recommended. Another popular choice is Mercury Messenger, which runs on Java. Or if you prefer IRC, there is Colloquy. Or you can get an open source clone of MSN called aMSN.