Microsoft Corp. today announced the immediate availability of the Windows 8.1 Preview, the next update of the Windows operating system, at the company's developer-focused Build conference. As part of the conference's keynote speech, the company outlined the reach, design and economic opportunities for developers to build differentiated, touch-based apps for the Windows platform, including new developer tools and increased support. Company executives also highlighted new top apps coming to Windows, including Facebook, Flipboard and NFL - clear evidence of the steady app momentum for Windows, which is experiencing the fastest growth across any platform. Microsoft CEO Steve Ballmer was joined on stage by Julie Larson-Green, corporate vice president of Windows, and other company executives to demo the Windows 8.1 Preview, focusing on key areas of personalization, search powered by Bing, increased functionality for businesses, new in-the-box apps and more. "With Windows 8 we built a new Windows, reimagined from the chipset to the experience. It was an ambitious vision, and with Windows 8.1 we refine it," Larson-Green said. "Windows 8.1 will support the widest range of tablets and PCs and demonstrates how responsive we can be for customers. The preview we are releasing today is an important step for partners around the world that are building the next generation of Windows devices and apps." DOWNLOAD: Windows 8.1 Preview Antoine Leblond, corporate vice president of Windows Program Management, also took the stage to outline how Windows 8.1 provides additional opportunity for developers to design, build and market their Windows Store apps. He reinforced the best-in-class economics - developers keep 80 percent of the revenue for the lifetime of the app once it crosses the $25,000 revenue threshold. He also highlighted new updates, including the following: Redesigned Windows Store. The Windows Store has been completely redesigned in Windows 8.1 to reach engaged customers and connect them more effectively and quickly to the apps they want. This includes increased merchandising opportunities for apps and better discoverability based on an individual's preferences, as well as new search controls from Bing in the user interface. App listings have a new layout with refined navigation and more related content. More monetization opportunities. Windows 8.1 delivers new opportunities for developers to build and monetize apps and engage users. Leblond introduced Windows Store gift cards, an easy way for consumers to purchase apps, books, games and content. Customers will be able to load their Microsoft Account with stored value in their local currency and make purchases online from the Windows Store. For developers in China, the Windows Store will support Alipay, meaning local developers will have new options to generate additional revenue. Leading experiences. Windows 8.1 offers developers a canvas to present and develop compelling app designs. Windows 8.1 apps can work together to share data, share the screen and deliver richer customer experiences across a range of devices, including new 8-inch-and-below form factors. Beyond Windows 8.1, Microsoft showcased how developers can take advantage of tools and resources across the company to build differentiated experiences for their customers across Microsoft devices and services, including the following: Bing as a platform. The new Bing platform builds upon the large investments Microsoft has made in the core technologies behind Bing.com to be embedded as intelligent services into Microsoft devices, Microsoft services and third-party apps that people use every day. In addition to providing the Search experience in Windows 8.1, Windows Phone, Xbox 360 and Microsoft Office, Bing Developer Services are now available that enable third-party developers to leverage Bing technology to create amazing experiences in their own services and Windows and Windows Phone applications. More information is available here. Releases of Visual Studio 2013 Preview and .NET 4.5.1 Preview. Timed to the next wave of Windows, Visual Studio 2013 offers the ideal toolset for building rich modern applications that run on Windows 8.1. With a range of new features, Visual Studio 2013 makes it easier and faster for developers to create applications and services using modern lifecycle practices that span mobile devices and the cloud. Microsoft also announced a preview of .NET 4.5.1, enabling developers to build next-generation applications for devices and services while innovating their existing core business applications. Visual Studio 2013 and .NET 4.5.1 previews are now available for download here. More on Visual Studio can be found here. Windows Phone developer opportunity. Microsoft today announced that shipments of Windows Phone grew six times faster than the rest of the smartphone market over the past year. Sprint also announced plans to add Windows Phone 8 to its 4G LTE network this summer with the HTC 8XT and the Samsung ATIV S Neo. With the release of Windows Phone 8, customers are now downloading more than 200 million apps per month and generating more than twice the daily app revenue. To help give developers the best return on their investments, the next release of Windows Phone will be designed to run the same apps that developers are building today and support the same familiar tools and skills. For a limited time, developers can register with Windows Phone Dev Center for only $19.