So what is Silverlight?

At its simplest, Silverlight is a plug-in that renders XAML-based user interfaces within a browser. Specifically, it supports modern incarnations of Internet Explorer 6+, Firefox 1.5+ & 2 and Safari 2 on the latest Windows (XP, Server 2003 and Vista) and Mac OS X platforms. Freely downloadable from Microsoft, the plug-in weighs in at a few megabytes, but it does contain some neat features, including the ability to update itself automatically and, more importantly, support for playing different media formats (VC-1, WMA and MP3) without requiring either the .NET Framework or Windows Media Player to be present on the client.

There is, however, much more to Silverlight than just a simple browser plug-in for playing some media files. For example, Microsoft is currently working on a new service, snappily entitled "Microsoft Silverlight Streaming by Windows Live", which provides an online home for Silverlight applications and their corresponding media content for those who don't want to set up their own media-streaming facilities.