Adium

Adium is a popular free software instant messaging client for Mac OS X that supports multiple protocols through the libezv (for Bonjour) and the libpurple (all other protocols) libraries. It is written using Mac OS X's Cocoa API, and it is released under the GNU General Public License, and many other licenses for components that are distributed with Adium. Many of the program's essential features are actually provided by plugins. The newest version includes support for file transfer, support for the Growl notifications system, Sparkle for program updates and support for encrypted messaging with the Off-the-Record Messaging library. Adium 0.88 was the first version compiled as a universal binary, allowing it to run natively on Intel-based Macs. Adium is also highly customizable through the use of resources its developers call "Xtras". The program can be customized by the use of hundreds of third-party Xtras that alter the appearance of emoticons, Dock icons, contact list styles, and messages styles. Adium can also be enhanced through the use of different sound sets. AppleScripts can also be utilized to automatically alter behavior in responses to certain triggers.