Introduced in 1980, the SOS operating system for the Apple /// used a hierarchical file system, a significant improvement over the flat filesystems used on the Apple II (by Apple DOS, Apple Pascal, and CP/M).

In 1983, Apple introduced the ProDOS operating system for the Apple II family, intended to replace Apple DOS. ProDOS used the same filesystem as SOS.

sosutil is intended to provide a command line interface to manipulate SOS and ProDOS disk image files. As of this writing, sosutil is only capable of printing the directory of such a disk image file.