Sport is a Xamarin.Forms app that manages athletes and the leaderboards they belong to. As a user, you can join different leagues and then challenge other league members above you. Sport facilitates sending and accepting challenges, posting the results of a challenge and re-ranking the leaderboard based on the winner.
Xamarin Sport shares nearly 94% of the code between platforms and is powered by an Azure Mobile Service back-end.
Feel free to check out the source code here: http://github.com/xamarin/sport