Spheres of Chaos... Mmmm. http://www.spheresofchaos.com/

That would be a great game to port to the web.

For what it's worth, I wrote a simplistic Osmos clone last year using 2D canvas drawing (not WebGL). It's fairly inefficient, but anyone's welcome to hack on it and make something cool with it.

http://stepheneisenhauer.com/demos/browsmos/

Well you can render many spheres with tiled rendering.

http://www.gamesfrommars.fr/demojsv2/