Metal

Apple's low-level API for programming the GPU on Macs, iPhones, and iPads.

Metal lets software talk almost directly to Apple's graphics hardware for both rendering images and general-purpose compute (like matrix math). It is Apple's alternative to cross-platform APIs like Vulkan, and it is the native path any GPU work must go through on Apple devices. In microZeus it serves both as a compute backend and as the target for visualizing neural-network activations.