Available, that is, to registered developers. A public beta program for Apple Seed participants will be arriving later this Summer. Here in the mean time, Apple has pushed OS X 10.11 15A204b (aka DP2) to devs and, more than a few of us, are hoping it addresses a range of stability and performance issues with Safari, Mail and a range of third-party apps.
For what it’s worth, updated Apple core apps including Safari 8.1, Mail 9, Photos 1.1 and Notes 4.0. Everybody’s favorite audio enhancer, Boom 2 doesn’t work with OS X El Capitan.
OS X El Capitan Mac Wallpapers? Get ’em!
Apple has also pushed watchOS Beta 2 and iOS 9 Beta 2 to developers. Again, at this early hour, little to nothing is known about these latest seeds.