Window Maker is an X11 window manager designed to give additional
integration support to the GNUstep Desktop Environment. In every
way possible, it reproduces the elegant look and feel of the
NeXTstep[tm] GUI. It is fast, feature rich, easy to configure, and
easy to use. In addition, Window Maker works with GNOME and KDE,
making it one of the most useful and universal window managers
available.

WWW: http://windowmaker.org/