While most developers who build apps for the Android today use Java, a new way to create apps using Microsoft's familiar C# language is now available thanks to TallApplications BV's Dot42, a new tool developed just for this purpose. TallApplications BV's Dot42 is a compiler that will allow you to code apps using Visual Studio while using the existing Android API libraries. And the licensing is simple with a community license that will allow you to use Dot42 in your own projects for free however creating commercial apps or publishing to the Play Store is currently prohibited. A professional license is available for a fee. See the details here.