Mac OS X Snow Leopard (version 10.6) was the seventh major version of OS X, and the sixth major upgrade to the OS since Mac OS X 10.0.
Snow Leopard was publicly unveiled on June 8, 2009 at the Apple Worldwide Developers Conference. On August 28, 2009, it was released worldwide, and was made available for purchase from Apple's website and its retail stores at the price of $29 for a single-user license.
Sales of Snow Leopard were significantly higher than that of its predecessors, in part due to the lower price as compared to past. The release of Snow Leopard came nearly two years after the introduction of Mac OS X Leopard (version 10.5), the second longest time span between successive Mac OS X releases.
Snow Leopard was less about features, and more about spring-cleaning the ageing OS. Support for older, PowerPC machines was dropped, and so the OS had a much smaller footprint.
Mac OS X Snow Leopard was soon removed from the Apple Store after the release of OS X Lion, however is now available again for the same price of $29, possibly to allow users to download Mountain Lion.