DOOM was definitely made with DOS in mind, but it also ran on NeXT from the beginning. It's pretty portable actually. Since you cited Fabien Sanglard, I guess I

DOOM was definitely made with DOS in mind, but it also ran on NeXT from the beginning. It's pretty portable actually. Since you cited Fabien Sanglard, I guess I should mention that his book about DOOM's source code (Game Engine Black Book: DOOM) explains how the portability stuff (as well as almost everything else) worked in great detail.