What .NET Standard is and how can it help the application design

While .NET Core is the best candidate for running your code almost everywhere, it is also true that we currently may need to run our code on different runtimes, such as .NET Framework for existing Windows applications, Xamarin for developing mobile applications, and Blazor for running code in the WebAssembly sandbox or on other older runtimes.

The first attempt to share compiled libraries across multiple runtimes was done with the portable class library, where the developer could only use the APIs that were available in all the selected runtimes. The resulting intersection was impractical because restricting the number of available APIs to just the common APIs was way too limiting. .NET Standard initiative was born to resolve this issue by creating versioned sets of API definitions for a number of well-known APIs. In order to be .NET Standard-compliant, any runtime must guarantee to implement that complete set of APIs...