In addition to iOS 10 and tvOS 10, Apple also released the third beta of macOS Sierra to developers on Monday. The update is available for registered Mac developers in either the Updates tab of the Mac App Store, or in Apple's Dev center.
Today's beta 3 release comes just about two weeks after Apple issued beta 2, and just a little more than a month after the original developer beta was made available. The software, of course, was first introduced during Apple's WWDC keynote.