This is piewm, a tvtwm with "pie" (i.e., round) menus.  You can change
"f.menu" and "menu" in your .tvtwmrc into "f.piemenu" "piemenu" in
.piewmrc and you will suddenly seeing lovely round menus.

It also has virtual desktops that you can "pull" things out, i.e.,
move the mouse into the virtual desktop window, grab a window with the
middle button, and move the mouse out, and then the window will appear
in the current screen.  This feature is exactly the same as tvtwm.