Elements for Sketch - High-quality UI Kits in Sketch, for free
Source Wireframe Kit - Library of 537 blocks for desktop and mobile prototyping
Tailwind CSS - A utility-first CSS framework for rapidly building custom user interfaces.
Contra Wireframe Kit - Open source wireframe kit for design and prototyping 🚀
DynaMaker - Cloud service for Visual Product Configuration with parametric geometry and CAD / BIM
Platforma - Wireframe library of layouts and UI elements