About
Final Fantasy is the game being ported here, originally released for the NES. ff1snes is a from-the-ground-up port of Final Fantasy to the SNES: no code was copied from the original NES version, though its disassembly was used as a reference during development. It's currently listed as semi-playable.
How it differs from the original
Unlike a straight ROM hack, the SNES version's code was written from scratch rather than reusing or directly porting the original NES game's code, though the original disassembly informed the implementation.