Libg3d is a glib-based library for loading and manipulating 3D objects. It supports a wide range of file formats for 3D objects and textures. Its plugin interface makes it easily expandable. The code has been split off from the g3dviewer project, which now depends on this library.
Mathnetics is an API for creating advanced, interactive, Web-based mathematical applications. It defines various important mathematical objects that are inter-related and on which many numerical calculations can be done. It also features rendering of 3D objects onto an SVG canvas (to do so, it includes certain utilities such as browser sniffing, DOM node selection, and DOM readiness detection), which is quite robust. A few basic 3D objects are given (Line, Sphere, Cube), but the user can define any 3D object desired as per the specification.
G3D is a C++ library for game developers, researchers, and students. It is a base of robust and high performance code common to most 3D projects. It is not a stand-alone graphics or game engine, but is a set of pieces to jump start your own engine or graphics project. The library has two parts: G3D for pure math, and GLG3D for interacting with hardware acceleration via OpenGL. You can use G3D without GLG3D if you want to use another 3D API (like DirectX) or don't like the OpenGL abstraction.
EQUINOX-3D is a 3D modeler with a very fast, fully integrated ray-tracer. It features read/write support for COLLADA, read support for Radiance's .hdr image format, 3DS (3D-studio) file format read support, multi-texturing, custom-programmable texture mapping, bump-mapping with automatic texture-space tangents, the ability to zoom into a region with "fly-to", and more. It includes a full runtime-class framework and a core design that allows for the addition of anything from a physics engine to a fully integrated renderer from a plugin. It is faster and more memory efficient than many other modelers.
QuartzCrystal is an application for rendering Quartz compositions to QuickTime movies and image sequences. It supports third party plugins (using both the official and unofficial API), as well as unsafe patches. It also supports spatial supersampling (antialiasing) and temporal supersampling (motion blur).
Octaviz is a visualization system for Octave. It is a wrapper that makes all VTK classes accessible from within Octave using the same object-oriented syntax as in C++ or Python. It also provides high-level functions for 2D and 3D visualization. Using those functions, most common visualization tasks (3D surface plots, contour plots, meshes, etc.) can be accomplished without any knowledge about VTK.
Seg3D is a volume editing and processing tool that combines a flexible manual segmentation interface with powerful higher-dimensional image processing and segmentation algorithms from the Insight Toolkit. DICOM, VFF, META, NRRD, and many other volume formats are supported. Users can explore and label image volumes using configurable, orthogonal slice view windows and 3D volume rendering.