At WWDC 2016 Apple announced the newest version of it’s Mac operating system. macOS 10.12 Sierra is the latest in a long line of OS X versions and has now been released to developers. It has also been renamed from ‘Mac OS X’ or ‘macOS’ to fit better with it’s other platform names (iOS, watchOS, tvOS).
Currently macOS Sierra is only available to paying Apple developers, with a public beta coming in July. However for those of you who want to get their hands on it right now, you can do just that. You don’t need to be a paying to developer to install and use macOS Sierra DP 1. All you need is the install file and a Mac to install it on. I would however not recommend installing this as your default operating system. It is best to install it within a virtual machine or on an external drive, due to the inevitable bugs you will run into.