Platforma - Wireframe library of layouts and UI elements
MontageJS - MontageJS framework is a platform to develop and create single page applications (which load single HTML page and dynamically update the app as the user puts in inputs or requests or interacts with the page.) with ease.
Source Wireframe Kit - Library of 537 blocks for desktop and mobile prototyping
Contra Wireframe Kit - Open source wireframe kit for design and prototyping 🚀
Form Wireframe Kit by InVision - A free wireframe kit from InVision
Apple Watch UI Kit - Quickly create Apple Watch app prototypes