Apple today released macOS 10.12.1 Sierra Developer Beta 4, which comes one day after releasing the third builds of iOS 10.1 and tvOS 10.0.1. This makes watchOS 3.1 beta 2 the oldest build in Apple Developer.
macOS 10.12.1 doesn't contain much in terms of new front-facing features (the release notes certainly don't say anything), as it's a minor update. It does, however, include support for the iPhone 7 Plus's Portrait Mode feature - which is being introduced in iOS 10.1 - in Photos.
If you're on the Public Beta, you'll likely be waiting until tomorrow for build 16B2548a, as Apple has been delaying them by one day. Oddly enough, today didn't see a public release of yesterday's iOS 10.1 build.
Safari 10.0.1 beta 4 is also available in Apple Developer. Of course, it comes pre-installed with the new macOS build, but you might want to use it on OS X 10.10 Yosemite or 10.11 El Capitan.
If you're on the Developer Beta, you can grab today's build by heading over to the Mac App Store and going to the Updates tab. Beta 4 will show up and you can follow the onscreen instructions to install it.