Android Nougat was officially released on August 22, 2016. It adds features such as multi-window support.
You can review the high-level changes at the Android developer website.
Of course, not all devices will get this update right away, even at release; others won't get it at all. Manufacturers and carriers often choose to add their own custom modifications, which tend to delay the official release.
When will each device get Nougat, either officially or unofficially, if ever?