Kadu project was started in 2001 as a simple KDE API try-out. Eventually, it became the most popular Gadu-Gadu client for Linux and other Unices (and MacOS X).

Kadu depends on Qt library version 3.x. Beginning with version 0.3.3 it does not require the K Desktop Environment libraries and can be used with other window managers.

Kadu supports Gnome and Window Maker as well. The core of Kadu is the libgadu library (its role being handling the network layer).

Here are some key features of "Kadu":

· Gadu-Gadu v6.0 support,
· contacts' groups with drag and drop support,
· icon depicting the sender (as in ICQ),
· KDE, Gnome2, Window Maker integration with tray,
· message encryption with OpenSSL,
· sms sending to all Polish mobile networks,
· file transfers (DCC),
· multiuser chats,
· event notifications by sound,
· event notifications by hint near icon in tray,
· notification about program updates,
· using descriptions from other programs (e.g. XMMS titles),
· detailed error notification,
· animated emoticons and support of original set of emoticons from GG,
· configurable windows look (colors),
· configurable chat history,
· advanced information panel - using html formatting
· advanced contact configuration,
· toolbar,
· multicolumn contact list,
· advanced network configuration (server IP and server port selection, proxy).