The fifth major update to Mac OS X, Leopard, contains such a mountain of features — more than 300 by Apple’s count — that it’s difficult to boil this $129 operating system release down to a few easy bullet points. Leopard is, at once, a major alteration to the Mac interface, a sweeping update to numerous included productivity programs, a serious attempt to improve Mac OS security, and a vast collection of tweaks and fixes scattered throughout every nook and cranny of the operating system.