SketchUp (formerly: Google Sketchup) is a 3D modeling program for applications such as architectural, interior design, civil and mechanical engineering, film, and video game design. A freeware version, SketchUp Make, and a paid version with additional functionality, SketchUp Pro, are available.
The program claims to be easy to use. There is an online open source repository of free-of-charge model assemblies (e.g., windows, doors, automobiles, etc.), 3D Warehouse, to which users may contribute models. The program includes drawing layout functionality, allows surface rendering in variable “styles”, supports third-party “plug-in” programs hosted on a site called Extension Warehouse to provide other capabilities (e.g., near photo-realistic rendering), and enables placement of its models within Google Earth.
A free version of SketchUp is available here. A heavily discounted version of SketchUp Pro is available for students and educators here.