The OpenGLEAN library pages provide documentation for the core library.
The gleandev library pages provide documentation for the OpenGLEAN Device library.
The gleanfonts library pages provide documentation for the OpenGLEAN Fonts library.
The gleanshapes library pages provide documentation for the OpenGLEAN Shapes library.
The redbook pages provide classic OpenGL examples as seen in the OpenGL "redbook". They have been adapted to use OpenGLEAN rather than old GLUT.
OpenGLEAN is a member of the GLUT (OpenGL Utility Toolkit) family. OpenGLEAN traces its codebase through OpenGLUT to freeglut. freeglut was written from scratch, but attempts to re-implement Mark Kilgard's original GLUT API.
OpenGLEAN provides an OpenGL 3D graphics rendering context attached to windows. It provides additional features that are either necessary in that capacity, or can only be done by OpenGLEAN, or which are easier to do inside OpenGLEAN than in a client. The name is supposed to suggest "lean", in contrast to "glut". Other members of the GLUT family have added feature on feature, without seeming to ever to remove features. Because of the manner of implementing them, some features were very cheap for GLUT to do. But because of the disjoint history, OpenGLEAN's menu code (to take a particular example) is lengthy, buggy, and not quite compatible. So, OpenGLEAN is going on a diet.
(This particular copy of this page is hosted by SourceForge, just to dispel any confusion.)