Apple Watch UI Kit - Quickly create Apple Watch app prototypes
MockMagic - A free, easy-to-use device mockup generator
Dimmy.Club - Device mockup generator for your website and app screenshots
Module 02: Layouts - Professional toolkit for UI/UX design
Mockup Generator by Pixeltrue - Create beautiful product mockups in just a few clicks
Mockup Generator - Create attractive product screenshots with just a few clicks