With the introduction of Windows 8 and Windows Phone 8 new kind of libraries, technologies and frameworks are available to write applications for these platforms. The framework for the Windows 8 Store Apps is not directly compatible with the .NET Framework for desktop applications, because it is based on native COM technology.

The question is now: Shall I write my code many times, for each platform again?

The answer is: No, not completely. With the concept of Portable Class Libraries, introduced with the new frameworks, you can write code once and use it on different platforms without changes.

How to use portable libraries and sharing code between Windows 8 and Windows Phone 8 is explained very well by two presentations from Microsoft’s BUILD 2012 developer conference:

Take a look and learn how to share your code for many platforms and save time and money!