Apple has seeded a new round of developer betas today, and as usual, there's something for everyone. Today's builds include beta 4 of iOS 10, macOS 10.12 Sierra, watchOS 3, and tvOS 10.
The news comes exactly two weeks after the third round. The second Public Beta for iOS 10 and macOS Sierra (there is no Public Beta for watchOS or tvOS) came around two days later, so expect Public Beta 3 within the next couple of days.
There is also a corresponding Xcode 8 beta that was released today. One of the main new features in Xcode 8 (aside from the obvious Swift 3) is support for the iOS 10, macOS Sierra, watchOS 3, and tvOS 10 SDKs, so as those OSes iterate, so must Xcode.
Interestingly, the one thing that is missing from today's round of betas is the new Apple TV Remote app. That's still on beta 3; however, Apple can seed that any time that it wants.
Update: The new Apple TV Remote app has been released, which is why there was no new beta today. You can download it here.