[Update: iOS 11 public beta 1 is rolling out now, but macOS High Sierra may not be available yet. macOS High Sierra public beta is still coming soon.]
Apple has released the first macOS High Sierra public beta for Mac. This allows users who are not registered developers to test pre-release versions of macOS with new features for free.
Prior to the public beta availability, macOS High Sierra has only been available to test with a $99/year developer account.
macOS High Sierra includes the Apple File System, HEVC support, Metal 2, improvements to Mail, Photos, and Safari, and more.
For more on macOS High Sierra, check out these stories:
You can register for the free public beta program here.