What is it?
Microsoft's Silverlight is a .Net-based plug-in for creating rich internet applications (RIAs). Inevitably dubbed a "Flash killer", Silverlight is promoted by Microsoft as "cross-browser, cross-platform, and cross-device", although (like Adobe's Flash and Flex), it contains proprietary elements, and the open sourcing has been done under Microsoft's own version of the public licence (MS-PL).
Microsoft itself is responsible for Windows and Mac OS X versions of Silverlight. Responsibility for Linux has been handed over to Novell's Mono project, and within a year, Linux users should have a feature-equivalent version. Citing precedents such as Windows Media Player, doubts have been expressed - most vociferously by Adobe - as to whether Microsoft will stick to its promise to maintain parity on all platforms. Microsoft has given assurances that it will.
For those already committed to .Net languages and development tools, Silverlight provides a way of creating RIAs without having to invest in new skills. Microsoft is also funding a project to integrate Silverlight development capabilities into the Eclipse IDE, which Microsoft claims "will open Silverlight development to any Eclipse user and help facilitate the integration of Silverlight-based applications into Java-based websites and services".
Where did it originate?
Silverlight's earliest incarnation, Windows Presentation Foundation Everywhere, was shown in September 2005. Silverlight 1.0 appeared in September 2007, and Silverlight 2.0 - originally 1.1, the release wise Microsoft users wait for - in October 2008.
What's it for?
Silverlight uses XAML (extensible application markup language, which Microsoft first developed for the Windows Presentation Foundation), as the user interface markup language. XAML has been optimised for .Net in ways that offer advantages to Visual Studio and Expression Blend users, but may present difficulties for non-Microsoft XML tools.
What makes it special?
Silverlight and Microsoft's ASP.Net Ajax have been designed as complementary technologies, which simplifies adding RIA features to existing web applications.
How difficult is it to master?
.Net language developers using Visual Studio 2008 should be productive with Silverlight almost immediately.
Where is it used?
Users include EasyJet, BSkyB and the Humana private healthcare group.
What systems does it run on?
Microsoft has pledged that Silverlight "will support all major browsers on both Mac OS X, Linux and on Windows", adding that "particular care is being taken to account for differences in platform and browser capabilities to ensure a consistent experience including Firefox, Safari and Internet Explorer". The Macintosh version of Silverlight 2 has the same feature set as the Windows version. Silverlight is available or under development for Windows Mobile and Symbian.
However, Silverlight development tools and environments, including the software development kit (SDK), run only under Windows Server 2008, XP and Vista.
Rates of pay
C# and ASP.Net web developers with Silverlight £28-40k.
The official Silverlight site has a range of tutorials and videos adapted to different skills and requirements, plus SDK, Expression Blend and Visual Studio tools downloads.