Licq has matured greatly from the simple ICQ clone it once was. As of now, it is at version 1.0.3, and supports many new features.
One of the most notable features of Licq is its plugin-based architecture. Licq supports plugins for a large portion of its functionality, the biggest of which is the interface. Anybody is free to write an interface for the Licq engine, which means Licq is no longer tied to the Qt toolkit, but has interfaces using GTK+, Gnome, and even a remote access interface that allows you to connect to Licq and control it over a network.
Licq also supports SSL encryption, has an extremely customisable event handling system, and uses nice plaintext config files that make tweaking stuff extremely easy. It is perhaps one of the best ICQ clients of all time.