Like every previous Windows Server release, Windows Server 2016 is jam-packed with new features and capabilities. While it is difficult to pick one single feature as the most significant, the new Nano Server deployment option is definitely a strong contender.
As you may recall, several years ago Microsoft gave us the option of deploying Windows in a lightweight Server Core configuration. Server Core deployments achieved their size reduction by sacrificing most of the GUI elements. Nano Server can be thought of as the next evolution in lightweight Windows Server operating systems.