The Khronos Group

Khronos Group - Conformant Products - OpenGL a list of graphics cards that conform to OpenGL by vendor and type for OpenGL 4.4 and higher.

ToGL a Direct3D to OpenGL abstraction layer from Valve Software. (License)

NVIDIA - OpenGL Driver Support

TinyGL is intended to be a very small implementation of a subset of OpenGL * for embedded systems or games. It is a software only implementation. Only the main OpenGL calls are implemented.

Learn OpenGL the online book for learning OpenGL.