If I google for list of X11 window managers "xwm", there's a reference in the first hit. The quotes around xwm are useful to screen out false positives.
xwm2
x2wm
xxwm
newxwm
xcbwm
ywm
wwm
notxwm
nxwm
nwm
tinyxwm
txwm
txfwm
xcbfwm
Taking a closer look at the original xwm, this project has long since been dead. i wonder if it would be fair to say the acronym itself could be used, as tribute to the original? or is that too confusing?