Microsoft has had evolving variations of the .NET framework over the years targeting specific platforms. Even within Windows, there were multiple .NET framework platforms depending on whether you were targeting ASP.NET, Windows Desktop, or Windows Phone.
When Microsoft bought Xamarin, they also inherited MONO, the UNIX implementation of the .NET framework.
Microsoft is now going to standardize the .NET framework across these variations in a new framework called .NET Standard.
This will provide a core set of libraries, APIs, etc. across platforms and workloads.
Using this approach, Microsoft is targeting library developers who want to create libraries that will work equally well across devices and operating systems through a common standard.
