Ayam is a free 3D modelling environment for the RenderMan interface. It features good RIB export, CSG (all RenderMan primitives supported), and NURBS modelling. Features instancing, arbitrary number of modeling views, object clipboard, independent property clipboard, n-level undo, console, and Tree-View with Drag-and-Drop support.
BRL-CAD is a powerful constructive solid geometry solid modeling system that includes an interactive geometry editor, ray-tracing support for rendering and geometric analysis, path-tracing for realistic image synthesis, network distributed framebuffer support, and image and signal-processing tools.
The Java 3D API enables the creation of three-dimensional graphics applications and Internet-based 3D applets. It provides high-level constructs for creating and manipulating 3D geometry and building the structures used in rendering that geometry. With this software, you can efficiently define and render very large virtual worlds. Blackdown's version of Java 3D uses the OpenGL low-level API to take advantage of 3D hardware acceleration.
Blender is a free 3D animation studio. It includes tools for modeling, sculpting, texturing (painting, node-based shader materials, or UV mapped), UV mapping, rigging and constraints, weight painting, particle systems, simulation (fluids, physics, and soft body dynamics and an external crowd simulator), rendering, node-based compositing, and non linear video editing, as well as an integrated game engine for real-time interactive 3D, and game creation and playback with cross-platform compatibility.
Coin is an implementation of Open Inventor. Open Inventor is the de facto standard API for retained-mode 3D graphics programming. Open Inventor has a highly extensible design, and has been designed to allow for rapid development of highly interactive 3D graphics applications in the fields of CAD, engineering, scientific computing, simulation, VRML, and visualization.
Convex 3D is a convertor, extractor, and viewer for such popular 3D formats as 3DS, Wavefront OBJ, and Lightwave 3D. It is written in C++ and uses a modular design. The package includes a standalone conversion tool (console) and GUI application (Qt and OpenGL are required) for viewing and more. It is not meant to be a modeler, but it can be a powerful tool to hack into 3D files made by 3rd party modelers.
Dice3DS is a set of Pure Python modules for dealing with 3D Studio format (*.3ds) files. It maps 3DS chunks into a hierarchical set of Python objects; it's a lot like how ElementTree works for XML files. Dice3DS requires Python 2.6 or higher and Numpy. Note that it is not a wrapper for lib3ds.