yep, was going to say that this is probably the real source behind the mystery. Early OS X is basically NeXT when Jobs came back to Apple. Doom was developed on NeXT, so id Software and Carmack already had a history of using BSD. They also released Quake for Linux around 1996, which may have used X11 (I cannot recall, maybe it just depended on 3dfx/nvidia without X11 at the time... it's been so long)

There are writings floating around from Carmack that he was playing around with the OS X prototypes back when it was called Rhapsody in the late 90s.

I also thought I read somewhere that Carmack persuaded Apple to bet big on OpenGL for OS X. (Ironic now that it's deprecated.)

Carmacks's blog post with his Steve Jobs stories, including him persuading Apple to adopt OpenGL https://www.facebook.com/permalink.php?story_fbid=2146412825...

Doesn't seem like a _bad_ bet considering it lasted 20 years and like 14 versions, though...

If it were up to me they wouldn't deprecate it, so I wouldn't call it a bad bet either.

The original quake on Linux used svgalib and was done by Dave Taylor and GAlexand (EFnet #c??)

I think that was the case for Doom, but for Quake 2 and 3 a SGI Origin 2000 was used.