Silverlight is a powerful development platform for creating engaging, interactive user experiences for Web, desktop, and mobile applications when online or offline. Silverlight is a free plug-in, powered by the .NET framework and compatible with multiple browsers, devices and operating systems, bringing a new level of interactivity wherever the Web works. Silverlight 4 adds a ton of new features, like webcam, microphone, and printing, to enable you to create incredible applications.
Microsoft Silverlight is an application framework for writing and running rich Internet applications with emphasis on multimedia, animations, and graphics, with features and purposes similar to those of Adobe Flash. The run-time environment for Silverlight is available as a plug-in for most web browsers. While early versions of Silverlight focused on streaming media, current versions support multimedia, graphics and animation, and give developers support for CLI languages and development tools.