The Universal Windows Platform project templates for Visual Studio 2015, allows us to create and run app on a Windows 10 Phone Devices, Windows 10 Desktop / Tables, on an Xbox or even on an IoT devices. When we develop an app in Visual Studio which is targeted for multiple devices, we can take help of List of Device Preview menu to see how your XAML based UI will render on various devices and screen sizes.
Open any of the XAML page for your Windows Universal App Project, go to the Design Mode, You will find the list of Devices and different form factors at the XAML Designer Window.
You can select your respective devices that you are targeting for ( Phone, Tablet, Xbox, IoT Devices etc.) from the drop down and in design time itself you can see / verify how the UI will render on other devices. There is also an option to select “Landscape” or “Portrait” view for each respective devices and form factors.
This is really a nice addition to the visual studio and great tool for Universal App. Developer.
Hope this helps.