NEXTStep, Mach microkernel and BSD userland. CUPS was never strictly Linux, nor was Webkit. Darwin, the underlying glue behind MacOS, is closer to FreeBSD than Linux, licensing being the motivation; it all depends on your definition of "free" as, for some of us - Cupertino included it would seem, having to release your mods as source isn't freedom at all.
Meh, whatevs, ancient history.
* Long-time *BSD user, jumped ship to De[bi|vu]an when the project became infested with divas.