If you're currently running the macOS 10.12 Sierra beta, it's time to check for updates, as Apple today seeded Developer Beta 7 and Public Beta 6. The build number is 16A304a.
macOS was the only beta that Apple offered today, deviating from its normal pattern of also seeding builds of iOS, watchOS, and tvOS. Of course, iOS 10 saw a similarly lone release on Friday, but we haven't seen any new watchOS or tvOS offerings in a week.
The release notes, as usual, list instructions for setting up the new auto-unlock feature, which is to set-up two-factor authentication on your Apple account. There's also about four pages of "notes and known issues".
It's worth noting that this is the first version of Apple's desktop operating system that will end support for older Macs since OS X 10.8 Mountain Lion. To run Sierra, you'll need a MacBook or iMac from late 2009 or newer, or a MacBook Air, MacBook Pro, Mac mini, or Mac Pro from 2010 or newer.
If you're already running the macOS beta, you can grab today's build by heading to the Mac App Store and going to the Updates tab. If you want to sign up for the Public Beta Program, you can do that here.