SpartaDOS X (or SpartaDOS 4.0) is a disk operating system for the Atari 8-bit family of computers, that closely resembles MS-DOS. It was developed and sold by ICD, Inc. in 1987-93.

Ten years later SpartaDOS X considered abandonware has been picked up by its enthusiasts, and developed further. These unofficial revisions, incorporating many of the utilities written since 1992, cleaning many identified problems and including numerous improvements, are: 4.31 (2005), 4.39RC (2006), 4.40 (a leaked-out beta, 2006), 4.41 (Feb. 2008), 4.42 (Dec. 2008), 4.4.3 (Apr.2011).

Changes in SpartaDOS X 4.43:

• SpartaDOS X should now work on SECAM Ataris (equipped with FGTIA).
• ARCLOCK.SYS will now reset the clock to 1-Jan-2000 00:00:00 when it discovers that the current setting is invalid (i.e. when the chip is first powered).
• Fixed buggy ATARIDOS.SYS code that was to be finding end of VTOC on MyDOS disks. Plus the driver will now report to the system the correct value of total sectors on disk (previously it was equal to the initial number of free sectors).
• DOSKEY has a new parameter: when you pass an /X switch at the end of  the parameter line while loading DOSKEY, a special shortcut will get activated: every empty line (containing EOL character alone) will be translated to a “DIR” command, and executed.
• COPY /M will now always clear the archived-bit (+A) on moved files.
• … more info here

source: trub.atari8.info wikipedia