Microsoft OpenGL is built into Windows NT and is designed to improve performance on hardware that supports the OpenGL standard. Cosmo OpenGL, on the other hand, is a software-only implementation specifically designed for machines that do not have a graphics accelerator.

Another standard that is popular for rendering 3-D images is Direct3D.

opengl.org 
Offers content for developers and end-users, along with daily news updates, tutorials, downloads, and documentation.

Silicon Graphics OpenGL Home Page 
Contains links to OpenGL documentation, FAQs, technical information, courses, news, and related sites.

Direct 3D analysis
This articles provides information on Direct 3D and OpenGL APIs.

OpenGL for OS/2 FAQ
This is a technial FAQ regarding OpenGL for OS/2.

OpenGL portability notes
This document presents information which will help to maximize OpenGL across different computer systems and within different configurations of similar systems.

Yahoo!'s OpenGL page
Yahoo!'s directory of OpenGL.

OpenGL at IBM
Contains information on OpenGL-related products, technical articles, newsletters, and activities, both inside and outside of IBM.

OpenGL projects and examples
Provides information on the OpenGL Utility Toolkit (GLUT) as well as summaries and examples of projects using OpenGL. Includes links to the Special Interest Group on Computer Graphics.