Apple only expose the OpenGL bindings via Cocoa. There are many libraries that will expose OpenGL for you. [SDL](http://www.libsdl.org/) and [GLFW](http://www.glfw.org/) are the two most prominent.
Exactly. With Go and GLFW I could write 3D GL apps running the same under Linux, Windows and Mac OSX. No need to mess with OS-specifics if you don't want to. SDL could do the same but since I didn't need Audio and all kinds of "media layers" and what not, GLFW seemed a lot leaner and immediately worked "out of box", too.
well I'm just sad for ogre3d. why only expose it via cocoa ?
You misunderstood him. He's not saying "only cocoa exposes gl", he said "cocoa only (as in just) exposes GL, but other cross-platform libs also expose it for you if you prefer not to deal with cocoa".