When it launched the beta versions of iOS 10 It's from macOS Sierra 10.12 at WWDC 2016, Apple reported that, in July, such systems would also be available to the general public. For that, it would be enough to become a participant in the Apple Beta Software Program (as its name implies, a company program for those who want to test the beta software / systems it launches).
Although many bet on the availability of OSs only at the end of the month, Apple today surprised and, two days after the release of iOS 10 beta 2 and macOS 10.12 beta 2 for developers, tried to put these versions also in the hands of any users courageous.
That's right: if you are a participant in the Apple Beta Software Program, you can now download the new operating systems and play with them a little while always remembering that the purpose of this early release is to help the company correct OS problems, sending feedback from all users. mishaps that are found (and be prepared, as there will be few especially when it comes to compatibility with third party apps).
My recommendation? Do not install these beta versions on your primary devices, the ones you use on a daily basis and depend on to perform important tasks. Speaking specifically on macOS Sierra, I suggest installing it on another partition, leaving the system completely isolated from its files. 😉
At WWDC, Apple also announced that both will be officially launched in the fall of the northern hemisphere probably around September / October.