Adobe Flash is the most popular competitor to Silverlight, supporting browser plug-ins and enabling the execution of rich content for the Web. Flash is not a new technology, and already has had a long life span as compared to Silverlight. But it does not have a huge community as expected; it may be because of the limited development tools which are not known to most developers. Flash uses ActionScript as the programming language and Flex as the programming environment, and most developers are far from these technologies.
For ASP.NET developers, to extend their websites using Flash content is not so simple. They need to learn a development environment like ActionScript and Flex. Apart from that, there is no way to generate Flash content using server-side .NET code, which means it’s difficult to integrate ASP.NET content and Flash content.
Silverlight aims to give .NET developers a better option for creating rich web content. Silverlight provides a browser plug-in with many similar features to Flash, but one that’s designed from the ground up for .NET. Silverlight natively supports the C# language, and uses a range of .NET concepts. As a result, developers can write client-side code for Silverlight in the same language they use for server-side code (such as C# and VB), and use many of the same abstractions (including streams, controls, collections, generics, and LINQ).