Marvel (mobile) - Turn sketches into prototypes (new iOS & Android apps)
Facebook Design - Devices - Images and Sketch files of popular devices.
Gomix - The easiest way to build the app or bot of your dreams
Smartmockups - Create stunning product mockups, easily and online.
Mockup Generator - Create attractive product screenshots with just a few clicks
Mockuuups Studio - Fast and easy way to create product mockups on macOS, Windows and Linux.