During the MIX 2010 keynote this morning, Microsoft will unveil the development platform for the Windows Phone 7 Series that will bring new applications to life. And guess what! The developer tools are free.

Microsoft has released a free comprehensive tool support package for Silverlight on Windows Phone 7 Series, available for download. Expression Blend for Windows Phone and a preview of Microsoft Visual Studio 2010 Express for Windows Phone will be also included as part of the download.

Of course there will be a Marketplace: Microsoft made available a new merchandising tool that will enable developers and designers to bring applications and games to market and increase the discoverability of applications with customers while supporting one-time credit card purchases, mobile operator billing and advertising-funded applications.

Silverlight 4 Release Candidate (RC): In addition, Microsoft announced a release candidate (RC) for Silverlight 4 which will enable developers to create and deploy even more robust applications and rich interactive experiences.

Expression Blend 4 Beta: Microsoft revealed a new beta for its design and development workflow tool which includes features such as Path Layout to enable developers and designers to build and animate innovative UI design via ground-breaking visual layout mechanism, without the need to write code. The beta also supports Silverlight 4, .NET Framework 4 and Visual Studio 2010.

UPDATE: The developer tools can be downloaded from MSDN or www.developer.windowsphone.com after 11 AM Pacific Time.