Kzephyr is a GUI front end for the zephyr chat system. It requires KDE 3.0 or later, as well as a working zephyr setup with tzc. If you don't know what this is already, you probably don't need kzephyr... It also needs the Boost library to compile.
The latest version is here.
Andrew Willmott has gotten it to compile on a Mac running OSX, fink, KDE, and X11: you can find a binary here and some compilation notes here.