Damian has put together a Xamarin Forms Stripe example app, based on their standard iOS and Android examples that let you browse products, choose a shipping address and method, add and select a payment method, and purchase the product.
A Xamarin Stripe example by Damian Mehers
Telerik has put together some real world Xamarin samples that are all open source. In addition, they have an step-by-step guide to building Telerik's Xamarin apps from backend to frontend.
Real-World Xamarin App Examples by Telerik
Suppose you have a collection of items and you want to display them in a ListView (Xamarin.Forms). The catch is that you want to change the display of each item depending on its state or some other code-based attributes. That's where DataTemplateSelectors come in.
DataTemplateSelector by Jesse Liberty