This is is an early version of Atari's Dos. The back of the package reads:
"Use Master Diskette II to load the Disk Operating System (DOS) II program into the computer's RAM memory. For details see the DOS II Reference Manual and the ATARI 810 Operator's Manual. Master Diskette II contains an improved version of DOS which provides faster data access and more utilities, and requires less resident RAM than the previous version. It also allows random access to data with the BASIC commands NOTE and POINT."