Docker is a docking application (WindowMaker dock app) which acts as a system tray for KDE and GNOME2. It can be used to replace the panel in either environment, allowing you to have a system tray without running the KDE/GNOME panel or environment.
A notification area (system tray) dockapp.
wmsystemtray is a system tray using the freedesktop.org system tray protocol designed as a Window Maker dockapp. It has the ability to display more than one dock window to make room for more tray icons, and the ability to scroll through the icons if more are present than will fit.
wmsystray is a program that provides a system tray for your X11 environment. wmsystray can be (and currently works best as) a Window Maker dock app.