Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Gmsh - Gmsh is a 3D finite element grid generator with a build-in CAD engine and post-processor.
FreeCAD - An open-source parametric 3D modeler
Altair - Visually Analyze Any Data at the Speed of Business
meshmixer - meshmixer is an experimental 3D modeling tool for making 3D mashups without too much hassle.
NETGEN - NETGEN is an automatic 3d tetrahedral mesh generator.