Source Wireframe Kit - Library of 537 blocks for desktop and mobile prototyping
FlowMapp - FlowMapp is a UX planning tool for creating visual sitemaps and user flow.
Contra Wireframe Kit - Open source wireframe kit for design and prototyping 🚀
A1 Sitemap Generator - A1 Sitemap Generator has been in active development and sold since 2005.
Platforma - Wireframe library of layouts and UI elements
Octopus.do - Build your website structure in real-time and rapidly share it to collaborate with your team or clients. Start prototyping websites or apps instantly.