RORDoom

RORDoom was an early attempt at implementing the Room Over Room effect in Doom. It was released shortly before Edge which provided a similar feature. Edge gained in popularity and RORDoom's authors stopped their effort.

In RORDoom, level designers could create sectors on top of other sectors, thus breaking the rule of non-overlapping areas. BSP tree pre-compilation was done as usual and RORDoom's engine detected subsectors that belonged to several sectors at loading time.