An object-oriented programming API
developed by SGI
for retained mode Computer Graphics
. It is also a file format
; in fact VRML
is very similar to the OpenInventor
OpenInventor allows you to describe a scene in terms of objects within the scene. It takes care of the rendering and low-level stuff for you. Objects need not only be simple things like: cylinders, spheres, polygonal surfaces, curved lines and surface; but also things like sensors (to detect when you've clicked on something), animation nodes (so that objects can be moved around easily) and the camera.
This makes it very easy to develop high-level 3D applications, without worrying about the nitty-gritty. OpenInventor has become very popular for this reason; and has become even more popular since SGI made it Open Source. OpenInventor applications are typically written in C++ (although there are other language bindings), and OpenInventor itself is written in C++. It runs on a lot of platforms, including Windows, Linux and IRIX.