Open Source Solid Modeling CAD
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.
SceneMaker is a 3D modeling tool, yet another desktop application for the Unix platforms.
Xi3D is an X3D renderer and browser for 3D Web content. It contains compliant parsers for VRML'97 types, a java scenegraph, XML bindings using SAX2, a content converter, full runtime and event model, DOM Level 2, vecmath