Kadu is an open source gadu-gadu protocol instant messenger client for Linux, BSD and Mac.
Since the version 0.3.7 Kadu uses a plugin system, called modules. Modules have a variety of functions: from the most basic, responsible for sound support or icon docking in the system tray etc...
# User-friendly, fast, stable and flexible
# Runs on Linux, BSD & Mac
# No adware.
# Open source