[aandon]

Google Sketchup is an unsophisticated but good quick-and-dirty modeling app. It wouldn't be a huge leap to see it built in a CSS framework like this.

[zurn]

SketchUp[1] is built for ease of use for in mind for people who are not 3D pros but there's actually quite a lot of clever things going on under the hood[2] so it would not be a weekend project to reimplement. But yes, a web based clone would be awesome.

[1] It's now owned/developed by Trimble, Google sold it to them ~4 years ago

[2] http://mastersketchup.com/sketchup-inference/