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.
pngcheck is the official PNG tester and debugger. Originally designed simply to test the CRCs within a PNG image file (e.g., to check for ASCII rather than binary transfer), it has since been extended to check and optionally print almost all the information about a PNG image and to verify that it conforms to the PNG specification. It also includes partial support for MNG animations.
The Visualization ToolKit (VTK) is an object oriented software system for 3D computer graphics, image processing, and visualization. VTK includes a textbook, a C++ class library, and several interpreted interface layers including Tcl/Tk, Java, and Python. VTK supports a wide variety of visualization algorithms including scalar, vector, tensor, texture, and volumetric methods. It also supports advanced modeling techniques like implicit modeling, polygon reduction, mesh smoothing, cutting, contouring, and Delaunay triangulation. Moreover, dozens of imaging algorithms have been integrated into the system. This allows mixing 2D imaging / 3D graphics algorithms and data.
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.
Agar is a toolkit for graphical applications. It features a modern GUI system with an unobtrusive API. Agar can use different graphics interfaces, such as SDL and OpenGL, and it has been ported to numerous platforms, including game consoles and embedded systems. Agar is implemented in C, but can be used from other languages.
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.