The .NET Standard Library is a formal specification of .NET APIs that are intended to be available on all .NET runtimes. The motivation behind the Standard Library is establishing greater uniformity in the .NET ecosystem. You just create a single .NET Standard Library and use it from any runtime that supports .NET Standard Platform. Yesterday, Xamarin announced support for .NET Standard Libraries for all Xamarin applications.
This includes creating and consuming local .NET Standard Libraries, but also adding .NET Standard Libraries from NuGet directly to your Xamarin apps. It’s now easier than ever to share code across all .NET platforms, including the recently introduced .NET Core and ASP.NET Core platforms.
It is now possible to add a NuGet to Xamarin applications that supports .NET Standard in both Xamarin Studio and Visual Studio. To create .NET Standard libraries in your Xamarin applications, download Visual Studio 2015 Update 3 and update to Xamarin 4.1.2 for Visual Studio in the Stable release channel.