The Windows Phone Developer Tools 7.1 Beta released today. Download them here. The tools enable you to get started developing applications for the next version of Windows Phone 7 Codenamed "Mango" and leverage new phone features while continuing to develop applications for Windows Phone OS 7.0. In addition to multi-targeting the tools offer some other great features:
Mango has numerous performance improvements such as fast application switching and the ability to run tasks in the background. In addition, Mango provides support for sockets and local database storage. For more information about the improvements and features in Mango, see What's New in Windows Phone Developer Tools. Mango also offers support for many of the features that were offered in Silverlight 4 such as improved data binding, RichTextBox and Viewbox controls, webcam and microphone capture. For more information about new features for Silverlight for Windows Phone, see What's New for Silverlight for Windows Phone.