SketchUp is a free 3D sketching program for the conceptual phases of design.
LEDAS Driving Dimensions for SketchUp is a plug-in for parametric modification of 3D geometric models in very simple and intuitive way....
Sefaira for SketchUp provides real-time energy and daylighting analysis.
Interactively render high quality 3D images direct from Google SketchUp.