WebKit is itself open source, so you can't discount that just because it was derived from another open source project.
Aside from LLVM/clang and WebKit (both of which are significant enough to deserve massive accolades all by themselves), you also have stuff like launchd (which didn't catch on outside Apple, but hardly their fault), libdispatch, and mDNS.
But apart from the sanitation, the medicine, education, wine, public order, irrigation, roads, the fresh-water system, and public health, what have the Romans ever done for us?
Historical note: Launchd might have caught on if Apple had open-sourced it sooner.
The author of the Upstart init system, Scott James Remnant, wrote in 2006,
"How does [Upstart] differ from launchd?
launchd is the replacement init system used in MacOS X developed as an “Open Source” project by Apple. For much of its life so far, the licence has actually been entirely non-free and thus it has only become recently interesting with the licence change.
[...]
Had the licence been sufficiently free at the point we began development of our own system, we would probably have extended launchd rather than implement our own. At the point Apple changed the licence, our own system was already more suitable for our purposes."
Aside from LLVM/clang and WebKit (both of which are significant enough to deserve massive accolades all by themselves), you also have stuff like launchd (which didn't catch on outside Apple, but hardly their fault), libdispatch, and mDNS.
But apart from the sanitation, the medicine, education, wine, public order, irrigation, roads, the fresh-water system, and public health, what have the Romans ever done for us?