Microsoft is making a remarkable re-entry into the mobile application development at Mix. Starting right now, development tools for Windows Phone 7 are available, for free, at developer.windowsphone.com. To get an idea of what the tools do, I would recommend you to look at the keynote that was broadcasted at live.visitmix.com, but the basic idea is that Windows Phone 7 development looks sweet. Web-based applications seem fairly easy to build, especially if you are already familiar with .NET. Blender, the tool used to build the (Silverlight) user interface is also provided for free. A handful of applications like FourSquare or Netflix (with streaming video) were shown, but overall this is looking very good for Microsoft, much better than it has ever been for them in the mobile space. This is big.