libQGLViewer is a C++ library based on Qt that eases the creation of OpenGL 3D viewers. It provides some of the typical 3D viewer functionality, such as the ability to move the camera using the mouse, which is lacking in most of the other APIs. Other features include mouse manipulated frames, interpolated keyFrames, object selection, stereo display, screenshot saving, and much more. It can be used by OpenGL beginners as well as to create complex applications, being fully customizable and easy to extend. It ships with many examples and comprehensive documentation.
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.
Jmol is a Free, Open Source molecule viewer and editor. It is a collaboratively developed visualization and measurement tool for chemical scientists. Jmol is an active project, and there are new features being added to it on a daily basis. Users are encouraged to modify it to fit their needs and to contribute their changes to the project.