Source Wireframe Kit - Library of 537 blocks for desktop and mobile prototyping
Invision - Prototyping and collaboration for design teams
Contra Wireframe Kit - Open source wireframe kit for design and prototyping 🚀
Mockuuups Studio - Fast and easy way to create product mockups on macOS, Windows and Linux.
Bloo Lo-fi Wireframe Kit - Open source wireframe kit for design and prototyping
Craftwork - A collection of User Interface resources made by Craftwork