WebGL 3D Engines and Tools
Pretty much all modern desktop browsers support WebGL Internet Explorer being a notable exception. Even then you can use hacks such as IEWebGL to get the support. Although the whole specification is quite new, there has been some interest. Google Maps is a nice example of a high profile application using it.
Since working with bare APIs is often quite arduous, many wrappers have emerged. Of these particularly three.js and PhiloGL have become popular. Libraries such as glMatrix,WebGLU, lightgl.js and csg.js provide helpers for particular purposes. It is even possible to emulate Canvas2D with WebGL by using webgl-2d.