Apple doesn't give us a rest this national Labor Day holiday. 😛
The third beta versions of iOS 11.4 (compilations 15F4061d and 15F4061e), from macOS High Sierra 10.13.5 (17F59b), from watchOS 4.3.1 (15T5555c) and the tvOS 11.4 (15L5560b).
They arrive about two weeks after the second betas, and they should not bring big news beyond what we already know: Messages in iCloud are again being tested on iOS and macOS, just like the AirPlay 2 protocol. In watchOS, we have a new incompatibility alert for old apps and a long possibility for third-party displays on Apple Watch.
Soon, these new test compilations should also be painted for members of the Apple Beta Software Program with the exception of watchOS, which does not participate in it.