Apple has started selling Mac OS X 10.6 Snow Leopard again on the Apple Store. This is great for those who want to carry on using Snow Leopard. It was the first Intel-only version of Mac OS X, but it could still run PowerPC apps using a layer of software called Rosetta which allowed this seamlessly. Mac OS X 10.7 Lion and later versions removed Rosetta completely so they cannot run PowerPC apps at all. For this very reason, there is a portion of Mac users that cannot and will not upgrade beyond 10.6.