"Adium is a free instant messaging application for Mac OS X that can connect to AIM, MSN, Jabber, Yahoo, and more. Notable Features include OTR Encryption, Tabbed Messaging, File Transfer, Webkit Message Display, Skinning/Customization." I use this program every day and highly recommend it. Check it out

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Colloquy is a beautiful IRC & SILC chat client for OS X. It supports all the colors from the windows IRC client mIRC, has a buddy list feature for your friends on IRC, and the ability to chat on multiple servers.

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"Fire is a free Instant Messaging client for Mac OS X. It supports the seven most popular Instant Messaging services: * AIM * ICQ * irc * Jabber * MSN * Yahoo! Messenger * Apple Bonjour"

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Meetro is dubbed a "location-aware social messenger." It "combines all the fun aspects of 'Social Networks', with all the real-time communications of 'Instant Messengers' wraps that around location, and finally adds two fist full’s of photos and profiles. I haven't tried this program personally yet, but it sounds like an interesting concept. Check it out and tell me what you think.

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Mercury messenger is a Java-based MSN client. It serves the MSN messenger network and offers basically all the same functions as MSN's own messenger. Since Mercury is Java based, it is capable of running on multiple operating systems including OS X.

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