Have a look at http://www.apple.com/opensource/ - which outlines the Open Source components that Apple use and contribute to. You're right - it might not be as much as some other companies (though I don't know if it's practically less than Google or Sun) but they are consistently among the largest participants in Open Source among large tech companies.
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?
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."
Do you have any access to Google Search API? Or BigTable source? How about Google Maps? Google Apps? What Google is releasing is "Chrome" which stole(as like your word) from WebKit, and Android. (which actually stolen from Sun, so still in lawsuit)
Well there's more. V8, Dart and Go. Maybe bunch of funny dead projects can be included. But I don't see much difference with LLVM/Clang case. Let's treat them just apart.
IMO, Google is worse than Facebook or Twitter in perspective of server-side software contribution.
Oh wow you capitalized "A LOT". I am sure you'll be able to list at least 30 large known open source projects actively maintained or contributed to by Apple.
