High Quality Content by WIKIPEDIA articles! Kadu is a Polish instant messenger using the Gadu-Gadu and Xmpp (since 0.9.0 version) protocol. Kadu is a free software, open-source software and does not contain advertisements (as opposed to the official Gadu-Gadu client, which is closed-source and adware). Since 0.6.5 version there is a Windows port available . Kadu is built on Qt.