Bishop3D is an interactive modeler and animation tool for the popular freeware raytracer POV-Ray™, a world-class renderer for creating three-dimensional photo-realistic images. Bishop3D allows you to model the scenes interactively and it will automatically generate the correspondent POV-Ray SDL script. It offers native keyframe animation support, POV-Ray SDL import and a powerful texture editor.

Bishop3D

http://durian.blender.org/

BRL-CAD is a powerful cross-platform constructive solid geometry solid modeling system that includes an interactive geometry editor, ray-tracing for rendering & geometric analyses, network distributed framebuffer support, image & signal-processing tools.

BRL-CAD

http://sourceforge.net/projects/brlcad/

Anim8or is a 3D modeling and character animation program which allows users to create and modify 3D models with built-in primitives such as spheres, cylinders, platonic solids, etc.; mesh-edit and subdivision; splines, extrusion, lathing, modifiers, bevel and warps,

Blender

http://www.anim8or.com/main/

AutoQ3D Community is an easy, light and fast 3D model editor tool that uses the full power of your PC´s graphics hardware, allowing you to rapidly prototype your 3D designs. Its interface is intuitive and easy to use and provided at no charge. It is released under the terms of the GNU General Public License so it will be free to use, modify and distribute within any educational, professionalor commercial purposes.

AutoQ3D

A free 3D modeling and animation software for aspiring game developers and modders. The Mod Tool is a free version of XSI for non commercial game creation. It is made for everyone needing a powerful 3D application to make and mod games. The Mod Tool plugs into all the major game engines and development frameworks for next-generation games, casual games, mods for existing titles and even Flash-based 3D games.

SOFTIMAG

http://softimage.com/downloads/XSI_Mod_Tool/default.aspx

K-3D is free-as-in-freedom 3D modeling and animation software. It features a plugin-oriented procedural engine for all of its content, making K-3D a very versatile and powerful package.
K-3D excels at polygonal modeling, and includes basic tools for NURBS, patches, curves and animation.

k-3d

http://www.k-3d.org/wiki/Main_Page

A free and open source 3D modeling and animation application which can be used for modeling, UV unwrapping, texturing, rigging, water simulations, skinning, animating, rendering, particle and other simulations, non-linear editing, compositing, and creating interactive 3D applications.

Blender

http://www.blender.org/