Three.js

Three.js brings 3D to the browser: interactive visualizations, product configurators, entire games, all running in WebGL. It wraps WebGL (the low-level browser graphics API that nobody wants to write by hand) into something you can actually build with.

Everything is free. MIT license, no paid tier, no cloud service, no account, and nearly two decades of development. The ecosystem is massive: loaders for every 3D format, physics engines, post-processing effects, VR/AR support. The documentation and examples library is one of the best in open source.

Self-hosting isn't really applicable. It's a client-side library you bundle into your app. Install via npm, import it, and start rendering.

The catch: the learning curve is steep if you've never touched 3D math. Cameras, lighting, materials, geometry. It's a different mental model from DOM manipulation. Performance optimization requires understanding the GPU pipeline. And the API surface is enormous, which means lots of ways to do things wrong before you find the right one. For simpler use cases like displaying a single 3D model, consider react-three-fiber which wraps Three.js in React components.