ApertureView (nuget): A Xamarin.Forms custom control that shows either the background or a child view using an aperture-like mask.  It is implemented exclusively in Xmarin.Forms and hence should run on all platforms where Xamarin.Forms is supported. Also, it is tiny.  Would probably look great on watches :D
Keywords: Xamarin.Forms|CusomControl|Aperture|CrossPlatform|aperture|csharp|custom-controls|design|gui|xamarin-forms