Apple contributes a decent amount back to open source. WebKit, launchd, mach, etc. See http://www.opensource.apple.com/darwinsource/ http://www.opensource.apple

Apple contributes a decent amount back to open source. WebKit, launchd, mach, etc. See http://www.opensource.apple.com/darwinsource/ http://www.opensource.apple.com/darwinsource/ http://developer.apple.com/opensource/index.html http://developer.apple.com/opensource/index.html and http://www.macosforge.org/ http://www.macosforge.org/ for a bunch their code.