Three.js
threejs.org
The WebGL renderer everyone builds on
ToolsOpen sourceJavaScriptWebGL
Penpot
Open-source design and prototyping
Live site
penpot.app
Preview Penpot inline
Loads the real site in a frame. Some sites block embedding — if it comes up blank, use Open instead.
What it is
Self-hostable, standards-based (SVG under the hood) and free. The credible open alternative when Figma's licensing or lock-in is a problem.
Tags
open-sourceself-hostedprototyping