Shockwave Flash (Flash before it was bought by Macromedia and then Adobe) laid the foundation for Rich Internet Application (RIA) development over ten years ago. Adobe claims that Flash Player currently is the most pervasive means of delivering media (animations, video) to over 98% of Internet-enabled desktops in mature markets. Even YouTube and MSN Video deliver video via the Flash player.
Microsoft released Silverlight in 2007 as a late response to Flash. While Silverlight currently lacks a wide user base, it does not take a big leap of the imagination to see how Silverlight might end up in the next Windows update. In the meantime, Microsoft is providing Flash Lite even on the Windows Mobile platform in order to play fair.