To use OpenJsCad go to: http://joostn.github.com/OpenJsCad/
The benefits over openSCAD are mainly in the language itself: you can use dynamic arrays for example, and solids can be stored in variables. It has built in support for 2D and 3D math, and handy features such as Connectors and Properties which make it possible to create more complex models.
Contributions are welcome, fork me on GitHub!
The only content here is in the gh-pages branch at https://github.com/joostn/OpenJsCad/tree/gh-pages
The actual CSG engine is in csg.js, while OpenJsCad.js contains the user interface.