Blender - Blender is the open source, cross platform suite of tools for 3D creation.
SelfCAD - SelfCAD is an online 3D modeling and slicing software.
SketchUp - 3D for Everyone
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.
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.
MilkShape 3D - The MilkShape 3D website has been down for almost one week.