The C# programming language (pronounced ‘see sharp’) can be used for many kinds of applications, including web sites, desktop applications, games, phone apps, and command line utilities. C# has been center stage for Windows developers for about a decade now, so when Microsoft announced that Windows 8 would introduce a new1 style of application, optimized for touch-based interaction on tablets, it was no surprise that C# was one of the four languages to offer full support from the start for these Metro style applications, as they’re called, (the others being C++, JavaScript, and Visual Basic).
Although Microsoft invented C#, the language and its runtime are documented by the standards body ECMA, enabling anyone to implement C#. This is not merely hypothetical. The open source Mono project at http://www.mono-project.com/ provides tools for building C# applications that run on Linux, iOS.