LibreCUDA is a project aimed at replacing the CUDA driver API to enable launching CUDA code on Nvidia GPUs without relying on the proprietary CUDA runtime. It achieves this by communicating directly with the hardware via ioctls, (specifically what Nvidia's open-gpu-kernel-modules refer to as the rmapi), as well as QMD, Nvidia's MMIO command queue structure. LibreCUDA is capable of uploading CUDA ELF binaries onto the GPU and launching them via the command queue.
Hopefully they have better defenses against legal action from Nvidia than ZLUDA did.
In the past, re-implementing APIs has been deemed fair use in court (for example, Oracle v Google a few years back). I'm not entirely sure why ZLUDA was taken down; maybe just to avoid the trouble of a legal battle, even if they could win. I'm not a lawyer so I can only guess.
Validity aside, I expect Nvidia will try to throw their weight around.
IIRC it wasn't legal action from Nvidia, but rather AMD pulling the funding that killed ZLUDA.
Yeah that is often the issue.
It is rare a single company owns all the IP on code. So its common that companies are not releasing code because they cannot.