From the site:
Adding a deck? Remodeling your kitchen? From simple to detailed, conceptual to realistic, Google SketchUp (free) lets you populate the world with true 3D objects. Want to build a fully dimensioned 3D model that can be used as the basis for your next do-it-yourself project? Google SketchUp's expanded feature lets you build in as much detail as your project requires.
Google SketchUp is free for personal use. No registration is required.