Microsoft's much-touted and much-anticipated RIA (rich Internet application) entry, Silverlight, lets Web developers and designers create "rich, engaging user experiences with 2-D graphics, animation, images, media, and video," to use Microsoft's own description. Silverlight competes in this arena with Adobe Flash and Flex, with OpenLaszlo and Curl, and with a variety of AJAX (Asynchronous JavaScript and XML) frameworks.

The Bottom Line Microsoft Silverlight 1.0 Microsoft, microsoft.com Very Good  8.4 criteria score weight Capability 8 30% Ease of development 9 30% Documentation 9 15% Performance 7 15% Value 9 10% Cost: Silverlight is free, but for advanced development and design you’ll probably want Microsoft Visual Studio and Expression Studio, which are commercial products. Visual Studio 2008 and Expression Blend 2 currently are available as free test versions. Platforms: Windows XP or Vista with IE 6 (or later) or Firefox 1.5 (or later) running on x86 or x64; Mac OS X 10.4.8 or later with Safari or Firefox 1.5 (or later) running on Intel or PowerPC. A Linux implementation is in the works. The Microsoft development and design tools require Windows. Bottom Line: Silverlight 1.0 has a small footprint and is useful for streaming audio and video and simple animations on Web sites, but its use of JavaScript limits its performance for applications that require significant client-side computations. Silverlight 1.1 has higher performance and supports compiled .Net languages, at the expense of a larger footprint. Developers familiar with Windows Presentation Foundation will find Silverlight easy to learn. Excellent development and design tools will make building Silverlight applications go quickly, as early adopters have seen. About our Reviews and Scoring Methodology

As I've written before, RIAs comprise a spectrum of application types and technologies. Silverlight is Microsoft's entry in the middle of the "weight" spectrum. It joins the Microsoft AJAX Library, which falls at the lightweight end, and Microsoft .Net Smart Client applications, which occupy the heavyweight end. Microsoft Silverlight 1.0 incorporates a subset of the .Net Framework and supports JavaScript. Microsoft Silverlight 1.1, currently in alpha tests, incorporates a larger subset of the .Net Framework and supports JIT-compiled C#, Visual Basic .Net, IronPython, and (eventually) IronRuby as well.

Unlike many of Microsoft's other offerings, Silverlight was designed from the ground up to be a cross-platform, cross-browser plug-in. It currently supports Windows and Mac OS using the Internet Explorer, Firefox, and Safari browsers. In the future, it will also support Linux and the Opera browser.

As you might expect from Microsoft, Silverlight is supported by excellent development tools. You don't absolutely need those tools: Silverlight 1.0 is largely straightforward enough that you could develop applications using free HTML and JavaScript editors if you wished, supplemented by a free XAML (Extensible Application Markup Language) editor, such as XAMLPad from the Windows SDK or Charles Petzold's XAML Cruncher. On the other hand, the time savings from using Visual Studio for development and Expression Studio for graphics design and video preparation should more than offset their cost.

The Silverlight 1.0 SDK can install a Silverlight JavaScript Application project template into Visual Studio 2005. For the best development experience, Microsoft recommends using Visual Studio 2008, which includes Silverlight 1.1 C# and VB project templates and is currently in beta test, and a preview version of Expression Blend 2. Setting up the Silverlight 1.0 JavaScript Application project template in Visual Studio 2008 takes some effort, which I discuss in this blog entry.

Silverlight is a browser plug-in and, as such, needs to be launched from an HTML page via JavaScript. The Silverlight runtime can parse and render XAML to the browser, animate XAML elements, and respond to user input and other events. It can also download and display media, and handle "ink" input from a pen, a touchscreen, or a mouse.

The Silverlight 1.0 plug-in provides mechanisms for setting and changing the XAML content to be executed by the runtime; for retrieving objects from the runtime; for manipulation of objects through JavaScript; and for downloading image, text, glyph, audio, and video content incrementally.

I found Silverlight development easy to learn, but I had a head start: I was already familiar with XAML, JavaScript, HTML, and Visual Studio. Expression Blend was new to me, but was similar enough to other graphical design tools that I didn't have to climb much of a learning curve. That said, I'm no graphical designer: I appreciate the division of labor between programmers and designers that is facilitated by having XAML and code-behind files.