Platforma - Wireframe library of layouts and UI elements
Mockups Design - Mockups Design is the most leading web-based application that comes with a vast collection of creatively design mockups for all kinds of products and devices.
Source Wireframe Kit - Library of 537 blocks for desktop and mobile prototyping
Mockuuups Studio - Fast and easy way to create product mockups on macOS, Windows and Linux.
Contra Wireframe Kit - Open source wireframe kit for design and prototyping 🚀
Mr. Mockup - Mr.