Several other back-ends exist, not all of them with the same level of polish or support as the NVIDIA and AMD back-ends.
Programming OpenCL GPUs in Julia is much more limited than other supported platforms. On recent versions of Julia, only OpenCL.jl is available. This package can be used to compile and execute GPU kernels written in OpenCL C.
Support for the oneAPI programming model is a work in progress, and can be found in the unregistered oneAPI.jl package. The package aims to offer the same level of programmability as the Julia CUDA stack, i.e., both offering an array-based and kernel programming model.