The Virtual Tab Window Manager. vtwm is a descendant of the reference X11 window manager, twm, enhanced to provide virtual desktops plus many other features, whilst remaining small and efficient.
Been using vtwm for quite a long time, very light weight. The beta version is .extremely stable, with the addition of True-Type font you cannot go wrong if you want a stable fast work environment.
Been using twm for years and have played with fluxbox quite a bit - discovered vtwm recently and have to say its faster than either and just as configurable! A single rc file makes it neat / tidy! Keep up the good work!
For a portable, clean, lightweight window manager, you need look no further. For glitz, you do.