SketchUp

*SketchUp is a 3D modeling (CAD) program for applications such as architectural, interior design, civil and mechanical engineering, film, and video game design. A freeware version, SketchUpMake, and a paid version with additional functionality, SketchUpPro, are available. SketchUp is currently owned by Trimble Navigation,[4] a mapping, surveying, and navigation equipment company.[5] SketchUp was independent from 2000 to 2006 and then owned by Google from 2006 to 2012.

SketchUp 4 and later support software extensions written in the Ruby programming language, which add specialized functionality. Such extensions may be made available to others on the SketchUp Ruby Forum.[22] SketchUp has a Ruby console, an environment which allows experimentation with Ruby.[23] The free version of SketchUp also supports Ruby scripts, with workarounds for its import and export limitations.*

http://en.wikipedia.org/wiki/SketchUp

cf Desktop Fab

Jun'2010: you can not only walkthrough the Google SketchUp 3D model, but you can do this all online, in a virtual environment, and it’s free with 3DVIA Scenes! (Virtual Reality)