Trillian was one of the original multi-protocol chat programs and a program I used back in the Windows days and continues to be very popular on Windows and OS X. Cerulean Studios is now bringing Trillian to Linux natively with a GTK+ port. This initial Trillian GTK+ version is mainly focused upon Ubuntu Linux support.
To some dismay, the Trillian for Linux version right now is limited to Trillian Pro subscribers paying $20 USD per year for the chat software. General availability of Trillian for Linux is expected at a later date.
More information on the Linux port of Trillian can be found via today's blog announcement.