gicq is an ICQ-compatible instant messaging client for Unix systems. It is based on the GTK toolkit. At the present time, the feature list is rather short. However, the most important stuff works - you can log on with an existing ICQ account, search for other users and add them to your contact list, and most importantly, send and receive messages. gicq uses libicq, which actually does most of the work. libicq is based on micq, a text-based ICQ client written by Matt Smith.
