RORDoom

RORDoom was created by Julian Aubourg and was the first Doom source port to have room-over-room capabilities. Based on Boom, it was released in 2000 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.