window-managers5
List of x window managers
Overview
/etc/X11/window-managers contains a list of paths to X window managers. If there is no $HOME/.xsession file available (or if the system is configured to ignore them) and executable by the user who started the X session, the /etc/X11/Xsession script will attempt to start each of the window managers listed in this file in turn, until it finds one that will run. X window managers may add or remove themselves from this file with the register-window-manager(8) command.
The path /usr/X11R6/bin should not be used. Use /usr/bin/X11 instead. Window managers in other locations should be referenced in a manner consistent with Debian policy.
Examples
/usr/bin/X11/mwm
/usr/bin/X11/fvwm2
/usr/bin/X11/twm
/usr/local/bin/my-wm