API Mapping tool is developed by Microsoft for both iPhone /iOS and Windows Phone 7 developers. The basic concept is that it helps developers discover the new WP7 platform. Acting more like a translation dictionary, iPhone / iOS developers can pick their specific apps, select the API calls, sort out classes, methods and events in Windows Phone 7.
Mapping is not yet available for all sorts of applications but for now it has to start with 3 categories (Network / Internet, User Interface and Data Management). Overall, a great news for developers. Still not a complete mapping tool, but again its a work in progress and right now they have launched it to gain more feedback from developers.
For feedback on this specific mapping tool, check this dedicated forum!
Don’t forget to check this Windows Phone 7 Guide for iPhone Application Developers.