We could see many initiative :
- http://spidergl.org/code.php (Nice Streaming Multi Resolution demo)
All the approach consisting in designing an interface to give access to OpenGL functions. So each initiative is a little High Level 3D engine.
The only drawbacks for the moment is that only nightly build of Firefox and Chrome have WebGL support but it's nice to see so many people want to have something 3D on the web !
But you can see other initiative in flash (no webGl, pure flash rendering) Here
You must definitively see this demo in flash : Here