[UPDATE 6/7: OS X 10.11.6 is now available for public beta testers as well.]
Apple has released the second OS X El Capitan 10.11.6 preview through the Mac App Store for developer testing. The software update to the Mac likely includes further bug fixes and performance improvements following similar releases throughout the year.
User facing features at this point are likely being saved for OS X 10.12, which Apple is set to introduce next month at WWDC and likely launch later in the fall.
Features we’re expecting to see debut in the next major Mac update include Siri on the Mac (finally) and a new version of iTunes. OS X could also be renamed macOS or MacOS to fit the iOS/tvOS/watchOS names.
The last feature update to the Mac came in OS X 10.11.4, which added password-protected Notes and Live Photo support in Messages.
Apple has also released tvOS 9.2.2 beta 2 for Apple TV.