Free Electron-based GUI prototyping tool that lets you wireframe interfaces, create mockups, and design diagrams without fighting with bloated commercial software or subscription fees.

Tired of paying monthly fees for Balsamiq or wrestling with heavy design tools just to sketch out a quick wireframe? Pencil gives you a clean, focused prototyping environment that runs everywhere thanks to Electron. It’s the kind of tool that gets out of your way so you can focus on ideas, not interface complexity.

What sets Pencil apart is its practical approach to real prototyping needs: tree-structured page management for complex projects, custom font embedding, a zip-based file format that handles large documents gracefully, and built-in stencils for everything from web UI to mobile mockups. The recent v3 rewrite ditched Mozilla XULRunner for modern Electron, making it significantly more maintainable and performant.

Perfect for product managers sketching user flows, developers mocking up features before coding, or anyone who needs quick visual communication without design tool overhead. With 9.5k stars and active development, it’s proven itself as the go-to open source alternative to expensive commercial wireframing tools.

⭐ Stars: 9500
💻 Language: JavaScript
🔗 Repository: evolus/pencil