I used to go daily into SGI developer pages, as they had nice documentation for C++, including the HP STL libraries (the original implementation for the STL proposal being discussed for ISO C++98).

I also had the opinion that the real cool 3D API was OpenInventor, not OpenGL, in a way true, as every engine ends up building their own scene graph from scratch.

One of the few UNIXes that was really cool to use.