>Thanks, interesting - but probably a non-starter. It appears to use it's own proprietry format to describe 'documents' with a limited number of export options.

Unlike RDBMSs, CAD systems AFAIK have not yet become commoditised. Especially if you're working with 3D modeling, my understanding is there are only a few big players that pretty much dominate e.g AutoCAD, Pro/Engineer etc. I don't know of any de jure standards for their documents, I believe they're de facto ( and proprietary ) in the same manner as Adobe PDF, Word DOC etc.

My ( limited ) experience is that tools and other parts of the ecosystem, in order to be successful, either work directly with documents in those proprietary formats, or can import/export them.

Having said that, is your objection to something like Sketchup, that its document format is not one of the industry standards, or that it uses a proprietary format at all?

There are some web-based CAD tools referenced at http://www.makerbot.com/blog/2011/04/12/online-cad-options/ .

I don't know if OpenGL is officially part of HTML5, but it looks like there's effort being put into making them work together - you can Google [html5 opengl]. OTOH I don't know how well the primitives available in OpenGL and/or HTML5 support the CAD-type functions you're contemplating.