Windows Runtime (WinRT) is Microsoft's new programming model for building Metro-style apps in Windows 8. WinRT uses an updated version of .NET's metadata format and allows code to be shared and used across languages like C++, C#, and VB. Developers with skills in C# and VB already have the ability to create Metro apps that are tailored for touchscreens and the Windows 8 interface. The document discusses WinRT components, portable class libraries, and using WinRT in both Metro and desktop applications.