UXpin - Design is really about solving problems. UXPin is the UX Design Platform that gets that right.
Source Wireframe Kit - Library of 537 blocks for desktop and mobile prototyping
Figma - Team-based interface design, Figma lets you collaborate on designs in real time.
Contra Wireframe Kit - Open source wireframe kit for design and prototyping 🚀
Moqups - The most stunning HTML5 app for creating resolution-independent SVG mockups, wireframes & interactive prototypes for your next project
Platforma - Wireframe library of layouts and UI elements