Fvwm3 is a multiple large virtual desktop window manager, originally (a
looooong time ago!) derived from twm.

Fvwm3 is intended to have a small memory footprint but a rich feature set,
be extremely customizable and extendible, and have a high degree of Motif
mwm compatibility.

Homepage:
https://github.com/fvwmorg/fvwm3
