Kadu is one of the most popular clients of the Gadu-Gadu network for Linux. It was created as a project using the API of the KDE desktop environment, but with time it became independent from it and can now be used on many other Unix-like systems as well as in Windows. The current version of Kadu supports Gadu-Gadu and Jabber/XMPP protocol (including Facebook and Google Hangouts).

It is a fully functional communicator equipped with support for conferences, animated emoticons, sound notifications, file transfer and chat encryption using OpenSSL. Sending SMS messages to users of Polish mobile networks is possible on the same basis as in the original Gadu-Gadu client. Everything is encapsulated in a configurable interface.