A program supplied on the AppleDOS 3.3 System Master disk that allowed files to be copied from pre-3.3 13-sector disks the the new(er) 16-sector disks used by AppleDOS 3.3 and ProDOS.
The compliment to this program is, of course, De-Muffin, which facilitated copying of files from 16-sector disks to 13-sector disks.