This document discusses Microsoft's shared Windows core across various platforms including Windows 8, Windows RT, Windows Phone 8, and Windows Server 2012. It highlights how the shared core allows for development of apps that can run reliably across over 1.3 billion devices. It also provides an overview of programming frameworks, languages, and APIs that enable development of portable apps across Windows 8, Windows Phone 8, and other platforms like iOS, MacOS, Linux, and Android.