XPlat Windows APIs
XPlat Windows APIs are designed to make it easier for developers adjusted to developing with the Windows Runtime APIs (UWP) to take those skills cross-platform with their applications in .NET.
As each application platform offers their own unique platform-specific APIs, XPlat attempts to bring all of those APIs under one umbrella using a UWP like API, allowing a developer to learn a single API which works with any application built for Windows and Xamarin for Android and iOS.
For a Windows developer, this is appealing as it allows you to easily migrate your existing Windows code to Xamarin shared code with minimal changes through the use of XPlat Windows APIs which mimic the UWP API alternatives.
Why should I use this project?
You've spent years developing Windows applications and you've been using the Windows Runtime APIs (UWP) to build modern app experiences. Now you want to take your existing apps and skills cross-platform with Xamarin, but you don't know where to start because you don't know what APIs to use!
I had this same problem!
That's where XPlat Windows APIs started, a set of APIs which mimic those Windows APIs but that are cross-platform, supporting both Android and iOS.
Use your existing skills and build epic cross-platform applications.