At last year’s Professional Developer’s Conference, Microsoft made a surprising move, announcing its Windows Presentation Foundation/Everywhere (WPF/E) browser plug-in. This will run multimedia applets everywhere, including Internet Explorer, Firefox, Windows and Mac. Even Linux is promised.

More recently, Microsoft added that WPF/E will include a subset of the .Net runtime engine, enabling C# and Visual Basic .Net code to run cross-platform, along with a native multimedia player for audio and video. The design tool for WPF/E will be Expression, while application developers will be able to code in Visual Studio.

It is a remarkable turnaround. For years, Microsoft has showed little interest in anything cross-platform beyond plain HTML and JavaScript served up by ASP.Net on Windows web servers. However, Microsoft is a late entrant to this field. Does WPF/E have any chance against Adobe’s well-established Flash player? It might. Flash has won over designers, but is less attractive for application developers, though Adobe is working hard to change that with its Flex development tools.

Flash runs ActionScript, a close cousin to JavaScript, whereas C# is arguably more suitable for applications that require a significant amount of code. “We don’t see people building complex applications with JavaScript,” said Microsoft developer Mike Harsh in a recent interview. Another advantage is that WPF/E has a native ability to render layouts defined in XML, whereas this feature has been bolted onto Flash at the tool level.

Java applets are another option for web developers, but Sun’s Java runtime is larger than WPF/E’s promised 2MB, and Java is less designer-friendly. Potentially, WPF/E could combine the design appeal of Flash with the application strength of Java.

There are also plenty of reasons why WPF/E might fail. Microsoft’s biggest challenge will be to get the runtime deployed. Adobe claims that some 98 percent of browsers already have the Flash player installed. Others will distrust the security of a Microsoft plug-in, or be sceptical about its cross-platform credentials and future. Judgment will have to wait until the first public previews this summer; final release is set for mid-2007.

In the past Microsoft has been characterised by its single-minded focus on Windows. Why does it now want to create a cross-platform runtime engine? It is the clearest sign yet that it can no longer base its entire strategy on the Windows client monopoly.

Microsoft’s problem is not only Apple and Linux chipping away at its desktop empire, but more seriously the rising importance of two other computing platforms where it is a minority player. The first is the web, and the second is mobile devices. It happens that WPF/E is also intended for device use, though Microsoft will probably struggle even more than Adobe to get its runtime embedded onto third-party hardware.

WPF/E is a welcome development, if only because it is time Flash had some healthy competition. It is also further evidence that the future belongs to cross-platform internet clients, not Windows desktops.