WebGL (Web-based Graphics Language) is a cross-platform, royalty-free web standard for a low-level 3D graphics API based on OpenGL ES 2.0, exposed through the HTML5 Canvas element as Document Object Model interfaces.

WebGL brings plugin-free 3D to the web, implemented right into the browser. Major browser vendors Apple (Safari), Google (Chrome), Mozilla (Firefox), and Opera (Opera) are members of the WebGL Working Group.
The specification is since 18 February 2011 in Final Draft (1.0) stage. WebGL is managed by the non-profit Khronos Group

Developers familiar with OpenGL ES 2.0 will recognize WebGL as a Shader-based API using GLSL, with constructs that are semantically similar to those of the underlying OpenGL ES 2.0 API. It stays very close to the OpenGL ES 2.0 specification, with some concessions made for what developers expect out of memory-managed languages such as JavaScript.

WebGL frameworks list (Khronos wiki page) : C3DL, CopperLicht, EnergizeGL, GammaJS, GLGE, GTW, O3D, SceneJS, SpiderGL, TDL, Three.js, X3DOM, WebGL Google Web Toolkit bindings, OSG.JS

And some cool demos and sources here and here !!!

Khronos WebGL home : http://www.khronos.org/webgl/

/**
 * Creates a webgl context.
 * @param {!Canvas} canvas The canvas tag to get context
 *     from. If one is not passed in one will be created.
 * @return {!WebGLContext} The created context.
 */
var create3DContext = function(canvas, opt_attribs) {
  var names = ["webgl", "experimental-webgl", "webkit-3d", "moz-webgl"];
  var context = null;
  for (var ii = 0; ii < names.length; ++ii) {
    try {
      context = canvas.getContext(names[ii], opt_attribs);
    } catch(e) {}
    if (context) {
      break;
    }
  }
  return context;
}