Disk Hacker is an FDS disk made by Hacker International that, presumably, allows a Disk System gamer to mess around with pirated disks, sort of like a hex editor.

Hacker International's Disk Hacker.

There are several versions of software capable of tampering with your FDS and games available on the black market. Another common name for this type of software is Copy Master, which allows you to play pirated games and tune your FDS.

Disk Hacker is the only such software known for being made by Hacker International.