This package contains xfwm4 which is the window manager for Xfce4. It is designed to run with the rest of Xfce4 but makes a capable window manager for GNOME or KDE.

Install xfwm4 if you want a small, resource saving window manager which complies to the standards defined at http://www.freedesktop.org/. Without xfce4 installed this only gives you a window manager not the full environment.