Alltray is a free opensource tool to dock any application with no native tray icon (like Evolution, evoluThunderbird, Terminals) into the system tray. A high-light feature is that a click on the ‘close’ button will minimize back to system tray. It works well with Gnome, KDE, XFCE 4, Fluxbox and WindowMaker.
Packman hosts a 1-click installer for Alltray.
Read more at www.susegeek.com