TaskyPro is a simple cross-platform todo/task application sample that allows you to track todo tasks. It illustrates proper application architecture layering and uses a common code base for the Business Layer, Data Access Layer, and Data Layer layers. It then separates out the User Interface and Application Layer into the appropriate device-applications.
The application runs on iOS, Android and Windows Phone 7 with a set of common classes shared across all three platforms. Open the TaskyMD_Mac.sln solution to see the iOS and Android apps on Mac OS-X and use the TaskyVS.sln with Visual Studio to see the Android and Windows Phone apps.
NOTE: it also supports some basic iOS localization to Spanish and Japanese.
The equivalent app written with Xamarin.Forms is called Todo.
Bryan Costanich, Craig Dunn