App building tools for Windows Phone 7 are coming on Sept. 16, Microsoft said Monday.

The tools have been available in beta test form for several months. The final developer tools will come out next month. Last week, Microsoft released a training course that includes 12 hours of training for developers.

Here is the Microsoft blog item detailing the new app building tools coming.

Microsoft is launching its new mobile operating system this fall to compete with the success of Apple's iPhone and Google's Android operating systems. The company had fallen behind in mobile development over the past few years and recently launched, then canceled a mobile phone project called Kin.

The success of Windows Phone 7 will depend on the apps, which is what drove iPhone and Android's popularity. What apps are available will depend on developers, which is why Microsoft is making a big deal about the tools.

Check out this Seattle Times story on why two Seattle developers from Mixpo decided to go with Google's operating system Android over Apple's iPhone.