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.
Drqueue is a distributed rendering queue. It helps manage jobs on a render farm. It works under Linux, Mac OS X, FreeBSD, IRIX, and Windows, supports Maya, Blender, Lightwave, Mental Ray, Bmrt (Renderman), 3Delight, and Pixie out of the box, and can support any other renderer or computing task that can be handled via scripting.
OpenSG is an Open Source scenegraph system. Its design goals include high performance, multithread-safe data handling, high flexibility, extensibility, and portability to Irix, Linux, and Windows. A number of computer graphics research institutions are actively working on moving the system beyond the state of the art to include features like clustering, subdivision surfaces, occlusion culling, and more.
PLIB is a set of libraries to write games and other realtime interactive applications that are 100% portable across a wide range of hardware and operating systems. It's used by Majik3D, FlightGear, and others, and includes libraries for GUI widgets, sound replay, geometry, scene graph, joystick, and fonts/text.
QGLViewer allows people programming in OpenGL to play around with three dimensional scenes or to write software that uses OpenGL. It provides a set of classes for camera control, as well as comfortable user interface that allows you to control your viewing parameters via mouse and buttons. A framework for camera paths and their interpolation is provided, as is a simple scene tree. QGLViewer is object oriented and programmed in C++ such that the programmer simply instantiates a viewer and connects it to their own render routines.
VisIt is an interactive parallel visualization and graphical analysis tool for viewing scientific data. Users can quickly generate visualizations from their data, animate them through time, manipulate them, and save the resulting images for presentations. VisIt contains a rich set of visualization features so that you can view your data in a variety of ways. It can be used to visualize scalar and vector fields defined on two- and three-dimensional (2D and 3D) structured and unstructured meshes. It was designed to interactively handle very large data set sizes in the terascale range, and works well down to small data sets in the kilobyte range.
freeglut is intended to be a 100% plug-compatible clone, and is released under the Xfree license. The GLUT (OpenGL Utility Toolkit) is a widely used library for doing window control, keyboard, and mouse input, and other basic functions for OpenGL programs. However, GLUT is not OpenSourced - although it's source code is available under a somewhat ill-defined set of restrictions. Hence, 'freeglut'.