Adium is a free and open source instant messaging application for Mac OS X, written using Mac OS X’s 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. Notable Features

• Open Source
• Support for multiple services
• Tabbed chat windows
• Mac OS X integration
• Address Book integration
• WebKit Message View: Theme your chat windows
• Combined Contacts: Merge your contacts so that each one represents a person, not an account
• A sophisticated events system (including Growl notifications)
• OTR Encryption
• File Transfer