As you may know, Kadu is an open-source instant messenger client written in Qt, having support for popular messaging protocols, like: GaduGadu, XMPP, GTalk, Facebook Messenger.
The latest version available is Kadu 3.0, which has been recently released, coming with changes. For more information, see the changelog.
The latest Kadu builds are available via PPA, so installing the software on Ubuntu is easy.
All you need to do is add the PPA to your system, update the local repository index and install the kadu package:
$ sudo add-apt-repository ppa:mati75/kadu
$ sudo apt-get update
$ sudo apt-get install kadu
Optional, to remove kadu, do:
$ sudo apt-get remove kadu
The installation instructions should work on Ubuntu 16.04 Xenial Xerus, Ubuntu 15.10 Wily Werewolf and derivative systems.