OpenSG

OpenSG is a portable scene graph system free ( SG) for creating real-time graphics programs, including for applications of virtual reality (VR). It is spread by the Open Source principles ( LGPL ) and may be used freely. It runs on IRIX, Windows and Linux and is based on OpenGL.

OpenSG should not be confused with OpenSceneGraph in which it is a different scene graph system, which is rather similar to OpenGL Performer.