Although the documentation has disappeared, it's still possible to develop and run code that does OpenGL/OpenCL. In fact, I'm writing OpenGL on a Mac as we speak. If performance isn't an issue, run a Linux variant in a VM. Performance in Parallels tracks pretty closely to running on the host OS.
Well, it does not look as if this question were to be answered properly any soon, so I will just leave here my best effort to answer it.
As far as I have seen, I have two promising possibilities for 3D/OpenGL and multimedia support that are cross-platform (including mobile) and full-featured:
Since my needs are rather low-level, I think I ...