Now UI Kit - A beautiful Bootstrap 4 UI kit. Yours free.
MockMagic - A free, easy-to-use device mockup generator
Landing UI Kit - Handcrafted UI components for landing pages
Platforma for iOS - The ultimate wireframe kit for app prototyping
UX Toolkit for Figma - Create beautiful user flow charts, sitemaps and wireframes
Smart Watch UI Kit - Helps smartwatch designers to design easily, 52 design