Mockup Generator - Create attractive product screenshots with just a few clicks
PSD to Sketch Design Converter - Convert a Photoshop design to a layered Sketch file for free
MockMagic - A free, easy-to-use device mockup generator
Zeplin - Collaboration app for UI designers & frontend developers
Mockuuups Studio - Fast and easy way to create product mockups on macOS, Windows and Linux.
Sketch Repo - Collection of resources for anyone who uses Sketch