OpenGL 2.x introduces a programmable pipeline with the new shaders system, and is notably available in mobile devices (OpenGL ES 2) as well as more recently in WebGL.
I was looking for Free documentation on this "modern" OpenGL 2.x, and was disappointed to find little of it: most of what I found was using the "legacy" 1.x API, and the rest was non-free. It's a gap to fill for the free gaming scene!
Consequently I started a on-going series of tutorials at WikiBooks (CC-BY-SA/GFDL) beginning from scratch with shaders:
The code samples are in the public domain:
Comments and contributions welcome
What do you think of it?