Prior to these off-cycle releases, Apple typically stuck to releasing updates roughly two weeks apart. Apple last updated public beta users a week ago. OS X El Capitan includes several performance and security improvements including better window management and a new Rootless security layer. The update also includes an overhauled Notes app, a smarter Photos app with extension support, and improvements to Spotlight including natural language search support.
OS X 10.11 Public Beta 3 can be found in the Mac App Store for Mac users running the public beta version of the operating system. In addition to running a Mac public beta for OS X El Capitan, Apple is currently running a public beta for iOS 9 as well ahead of its release. Mac users can learn more about Apple’s Beta Software Program including the various public betas of OS X and iOS.
Source : http://9to5mac.com/2015/07/29/os-x-10-11-public-beta-3/#more-390657