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.
ngPlant is a plant modeling software package. ngPlant interactive tool can be used to create 3D models of different plants and trees. ngPlant software libraries can be used by developers in their 3D applications, or plant modeling plugins.
Ayam is a free 3D modelling environment for the RenderMan interface.
Earth orbits and coverage display in 3D on your laptop.
SaVi - simulate Iridium, Globalstar, O3b, Sirius Radio, GPS, Galileo and other satellite constellations, modify them, or design your own. Uses Tcl/Tk and Unix libraries; 3D viewing option requires Geomview running on X Window.
3D rendering and scene graph library
High-level 3D graphics library. Supports retained and immediate mode rendering, an extensible file format, plug-in renderers, a wide range of high level geometries, hierarchical models, and a consistent and object-orientated API.
X3D is the open-standard format for 3D graphics scenes on the Web.
Extensible 3D (X3D) Graphics is a royalty-free International Standard for real-time interactive 3D graphics on the Web, providing unsurpassed interoperability for 3D communications on the Web. This project includes source for example X3D scene libraries and multiple X3D codebases produced by Web3D Consortium members. All open-source contributions are welcome.
The Open Model API (OMA) isn't only an API, it's also a toolkit. OMA supplies conversion tools for 3D models as well as a developer library inspired by OpenGL's state machine design.
CSG for jMonkey
Expanded Constructive Solid Geometry support for jMonkey. CSG supports boolean operations on primitive shapes, building up a complex surface from the addition/subtraction of simple cubes, spheres, etc. Check out the jMonkeyCSG website for more details.