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.
ArrayFire is a general-purpose software library that targets CPUs, GPUs, and other accelerator hardware. The ArrayFire.jl package provides a Julia interface to this library, and makes it possible to program accelerators using an array abstraction built on the ArrayFire library.
The NEC SX-Aurora Tsubasa is a PCIe card which works as a Vector Computer. It can be programmed from Julia using the VectorEngine.jl package, which at the moment requires a custom Julia build using a LLVM fork. Support is expected to improve due NECs involement.