Version 10.6 of Mac OS X, code-named Snow Leopard, was released on August 28, 2009.
Snow Leopard introduces focuses on improving performance, efficiency and reducing its overall memory footprint compared to its predecessor Leopard rather than new end-user features.
Version 10.5 of Mac OS X, code-named Leopard, was released on October 26, 2007.
Leopard introduces a significantly revised desktop, with a redesigned Dock as well as Stacks, a semi-transparent menu bar. Other notable features includes an automated backup utility called Time Machine, support for Spotlight searches across multiple machines and the inclusion of Front Row and Photo Booth, which were previously only included with some Mac models.As with any new major version, there were with Leopard healthy reservations initially including third-party software catching up to be fully compatible; our Director's Blog illustrates some. At a reasonable time, LSCR began recommending Leopard.
Leopard is presently at version 10.5.5, released on September 16, 2008.
The following articles provide information on previous versions of Mac OS X.