There's open-source graphics drivers that use NVIDIA like 'nouveau', which in my experience are much better than the proprietary nvidia graphics drivers on linux. Otherwise, I believe CUDA exists and remains proprietary because ISAs change by GPU generation, and because NVIDIA has a habit of patching graphics bugs outside its API for gaming customers, both of which lead to tight coupling between client libraries and the underlying hardware.
I know about nouveau and respect its developers so much. Trying to make it work despite an active resistance from NVIDIA itself - it requires some patience and rigor. The stance on providing firmwares to the project is ridiculous. I believe, NVIDIA invented the whole signing feature just to undermine nouveau efforts, using security just as a pretext (as many vendors do).
