I noticed there is some confusion about terms Metro, WinRT and what they mean and how they are different on Windows 8. I thought it would be useful to clarify these.
Metro is design language, a style used to define an application appearance. You can have Metro design made in WinForms, WPF, Silverlight, HTML or WinRT. In fact you can make Metro design using any language or platform that lets you create visuals on screen. And indeed there are Metro designs used for Android apps.
WinRT is platform. In same way we have today WinForms platform which is GDI based, WPF platform and Silverlight platform, in Windows 8 we get new WinRT platform. WinRT provides third XAML based User Interface model for developers.
WinRT default design is Metro. This is akin to WinForms using default “battleship gray” design or WPF using, um, whatever that design is called, I guess battleship gray as well…
WinRT is available on Windows 8 only and it is used to build so called Windows 8 Immersive Apps. These apps run in Windows 8 tablet mode. Apps that we build using all platforms we have today run in Windows 8 desktop mode. The only way to build apps for tablet mode in Windows 8 is to use WinRT.
Let me know if you have any questions or if this is not clear enough. I will update the post with your feedback.