Instantbird

Instantbird is an instant messaging client for AOL, MSN, Yahoo!, Google Talk, Twitter, Facebook, Jabber, IRC, and ICQ. It is an open-source project, based on Mozilla's XULRunner and the libpurple library used in Pidgin. With features such as being able to connect with multiple accounts at the same time and a large collection of add-ons, Instantbird aims to redefine the way instant messaging is used, so that it works the way you want.