UWP on Xbox One samples
There are several cross-platform UWP samples that have been optimized for Xbox One when running on that platform. You can browse the code on GitHub, read through the readme's and wiki's, and clone the projects to your machine.
TVJS includes support for automatic controller navigation, rich media playback, search, and more. You can use TVJS with your hosted web app just as easily as with a packaged web UWP app with full access to the Windows Runtime APIs.
The News Experience
The News Experience, Fourth Coffee, is a sample news app that works across desktop, phone, and Xbox One and offers a premium experience that takes advantage of each device's strengths. On Xbox, it's optimized for gamepad, the UI is tailored to the 10-foot experience, and it keeps content in the TV-safe area, among other optimizations. See the blog post for more information.
Gamepad-style navigation (XAML) sample
The Gamepad-style navigation (XAML) sample is a UWP sample that shows ways of improving directional navigation in your app. While this is also applicable to desktop applications, where a customer may want to be able to use a keyboard to navigate the app, it's especially relevant to Xbox applications, where the main method of input is gamepad or remote control.