In version 3.0 Microsoft has focused on bringing WinJS cross platform. Now a developer could write an app for the iPhone using WinJS and use the same code on their website, or Android version. This gives developers the ability to reuse more of their code when making their apps on different platforms. More reused code could mean faster ports, and easier updating.
Its not all about apps though. WinJS 3.0 also works on the web across browsers. Now the same code can be used to deliver beautiful, simple and consistent controls and UI elements regardless of browser. Again, this is less code for developers to write and less troubleshooting and testing meaning better websites in a shorter time.
Not only can WinJS 3.0 deliver the same experience on a wide variety platforms, but you don't have to include the entire library into your project. Now WinJS has been broken into several dozen modules which can be applied independently to keep the final project small and efficient. Smaller, more efficient, consistent and cross platform; Can you ask for any thing else? WinJS is available today from a variety of sources, follow the source link below and get it for yourself!