3D Modelling

BRL-CAD
An Open Source CSG solid modeling system with ray tracing support for rendering and geometric analysis, network distributed framebuffer support, image-processing and signal-processing tools.
http://brlcad.org/

J&L Associates
Developers of the ActiveSolid 3D solid modeling, CAD prototyping and mark-up sharware application and the underlying BspSolid modelling library.
http://activesolid.ncf.ca/

MINOS
A free 3D solid modelling software offering fast hidden line removal, topological functions, 3D geometric constructions, IGES support, shading, printing, hatches, and line constructions.
http://www.le-boite.com/minos.htm

RogCAD
Keyboard driven modeling software which supports complex curved surfaces.
http://rogcad.com/

Shapeways
Ships physical realizations in a variety of materials of uploaded models. Includes available materials, formats accepted, pricing, tutorials, and support.
http://www.shapeways.com/

solidThinking
Modelling software that supports NURBS, polygonal modeling, and subdivision surfaces, available for Windows and Macintosh.
http://www.solidthinking.com/

TouchCAD
3D modeling, unfolding and unwrapping program for Macintosh and Windows.
http://www.touchcad.com/