OS X El Capitan

OS X El Capitan ( ) (version 10.11) is the twelfth major release of OS X (now named macOS), Apple Inc.'s desktop and server operating system for Macintosh computers. It was released after OS X Yosemite and focuses mainly on performance, stability and security. Starting with OS X Mavericks, future operating systems of OS X were named after regions of Northern California. El Capitan was named after a rock formation in Yosemite National Park, to highlight a refined version of its predecessory, OS X Yosemite. 
El Capitan is the final version to be released under the name OS X. Its successor, Sierra, was announced as macOS Sierra. El Capitan received much better reviews when compared to Yosemite.
The first beta of OS X El Capitan was released to developers shortly following the WWDC keynote on June 8, 2015. The first public beta was made available on July 9, 2015. There were multiple betas released after the keynote. OS X El Capitan was released to end users on September 30, 2015, as a free upgrade through the Mac App Store.