MockMagic - A free, easy-to-use device mockup generator
Contra Wireframe Kit - Open source wireframe kit for design and prototyping 🚀
Platforma for iOS - The ultimate wireframe kit for app prototyping
Platforma - Wireframe library of layouts and UI elements
Smart Watch UI Kit - Helps smartwatch designers to design easily, 52 design
Craftwork - A collection of User Interface resources made by Craftwork