If memory serves well (I only have 3583 bytes free ;) Enlightenment was one of a generation of X window managers that implemented bitmapped theming, for example

If memory serves well (I only have 3583 bytes free ;) Enlightenment was one of a generation of X window managers that implemented bitmapped theming, for example fvwm, fvwm95, aftertep, windowmaker, icewm... it's just that Rasterman took the bitmapping to the next level.