mumax3 is a GPU-accelerated micromagnetic simulation package that solves the Landau-Lifshitz-Gilbert (LLG) equation. It is structured as a monolithic application with a custom scripting language (.mx3), a simulation engine, a CUDA compute backend, and several command-line utilities for conversion, plotting, and distributed execution. The simulation data flow involves compiling an .mx3 script, setting up the simulation mesh and material parameters, and iterating the LLG equation using GPU kernels for torque calculation, energy minimization, and output generation. The codebase demonstrates high craftsmanship in several areas: a cleanly abstracted multi-component array (data/slice.go), an embeddable script interpreter (script/), a transparent HTTP filesystem (httpfs/), and comprehensive low-level CUDA driver bindings (cuda/cu/). The auto-generation of CUDA kernel wrappers (cuda2go) is a sophisticated pattern that bridges Go and GPU code, though it results in significant code duplication. While actively maintained, the project shows signs of technical drift, including reliance on legacy Go tooling (gccgo, go vet), Travis CI, and hardcoded PTX assembly for a wide range of GPU architectures. The auto-generated wrapper files are a maintenance burden, but the core physics and simulation logic remain robust and well-tested.