I ported a decades-old piece of scientific software (Delft3D — Deltares' Fortran hydrodynamics engine) to run natively on Apple Silicon. From my phone, mostly, because I could (and because AI could). Runs pretty decently on a Mac Studio M3 now.
It was officially Intel-compiler + Windows/Linux only; the port gets it building with gfortran on macOS/arm64, PETSc+MPI solver and all. Fable and GPT-5.6 chewed through the compiler warnings, dependency hell, and portability bugs largely on their own. 30 or so bugs uncovered and fixed along the way, several of them real and platform-independent.
I'm not a C or Fortran dev. Mostly I argued with the agents about benchmarking methodology and told them to re-measure when the numbers looked off. The rest was up to them. Still amazed about this AI thing going on