SculptGL is a web sculpting application, powered by WebGL and JavaScript.
The source code can be found on github here.

Shortcuts so far :

SculptGL is available on the chrome web store.

If you want a standalone version, it's here (nodejs version, so same performance as the web version).
Also, keep in mind that I often update the web version (unlike the standalone version).

For the old SculptGL version you can play with it here.
You can visit the old branch on the github page.