KWin/X11 is an X11 window manager and a compositing manager. Its primary
usage is in conjunction with a Desktop Shell (e.g. KDE Plasma Desktop).
KWin/X11 is designed to go out of the way; users should not notice that
they use a window manager at all. Nevertheless KWin/X11 provides a steep
learning curve for advanced features, which are available, if they do not
conflict with the primary mission. KWin does not have a dedicated targeted
user group, but follows the targeted user group of the Desktop Shell using
KWin/X11 as it's window manager.

KWin is not...
 * a standalone window manager (c.f. openbox, i3) and does not provide any
   functionality belonging to a Desktop Shell.
 * a replacement for window managers designed for use with a specific
   Desktop Shell (e.g. GNOME Shell)
 * a minimalistic window manager