Blender - Blender is the open source, cross platform suite of tools for 3D creation.
SketchUp - 3D for Everyone
Fragmotion - Fragmotion is a 3d modeling and animation software.
AC3D - AC3D is a 3D software for games, virtual reality and flight simulation, scientific, medical and general data visualisation, rapid prototypes of 3D designs, 3D printing, Google Earth, X-Plane, Second Life and more.
PathEngine - PathEngine is a middleware toolkit for the implementation of intelligent agent movement, built around and implementation of points-of-visibility pathfinding on 3D ground surfaces.
FreeCAD - An open-source parametric 3D modeler