OS X 10.11 El Capitan was first unveiled in June and introduces several feature and performance enhancements to the Mac.
For instance, the Mac’s full screen feature adds support for running two full screen apps side-by-side while Spaces and Mission Control have been refined. Spotlight search includes additional sources for finding data and supports natural languages inquiries. System apps including Mail and Safari receive feature improvements like better full screen multitasking and the ability to pin tabs when browsing. The Notes app gets completely overhauled with new rich media features and more.
Mac users can learn more about Apple’s Beta Software Program including the various public betas of OS X and iOS here.