XNA Game Studio

XNA Game Studio is an integrated development environment (IDE) that includes tools and code development libraries that hobbyists, students and other nonprofessionals can use to create computer games for Microsoft Windows and X-Box 360.
To get started with XNA Game Studio, you'll need to have a basic working knowledge of C# and object-oriented programming (OOP). The basic version of XNA Game Studio, which includes Visual C# 2005 Express, development tools and a runtime environment, is free of charge. Debugging can be done from the Windows desktop. XNA Game Studio does require a Direct 3D video adapter card that can support Shader Model 1.1 or later, along with the latest DirectX runtime updates, so some hardware expense may be involved.

If a programmer wants to develop, debug or play games on an Xbox 360, however, he or she must subscribe to the XNA Creator's Club. Friends or family that want to play a game created with XNA Game Studio on Xbox 360 must also have XNA Game Studio installed on the gaming console, along with the runtime environment and a subscription to creator's club. Games developed with XNA Game Studio cannot be shared using any removable storage medium or burned to disc.

Games created with XNA Game Studio or XNA Game Studio Express for Windows can be sold commercially. Games created for XBox 360, however, are limited to non-commercial use by the Microsoft EULA and technical requirements.

With this initiative, Microsoft hopes to attract developers to create games for Windows and its popular Xbox 360. Programmers that create and upload games to the Creators Club community will have the opportunity to receive up to 70% of the revenue from sales of the applications.

Source: http://whatis.techtarget.com