Mac OS X Lion (version 10.7; marketed as OS X Lion) is the eighth major release of Mac OS X, Apple's desktop and server operating system for Macintosh computers. A preview of Lion was publicly unveiled at Apple's "Back to the Mac" event on October 20, 2010. It brings many developments made in Apple's iOS, such as an easily navigable display of installed applications, to the Mac, and includes support for the Mac App Store, as introduced in Mac OS X Snow Leopard version 10.6.6. On February 24, 2011, the first developer's preview of Lion (11A390) was released to subscribers of Apple's developer program. Other developer previews were subsequently released, with Lion Preview 4 (11A480b) being released at WWDC 2011.