Atari 8-bit / Bank Street Writer and DOS.
I have ATR (Atari disk images) for Bank Street Writer (which is interesting to compare to BSW Plus for the PC) and Atari DOS 2.5 among others. I noticed Atari DOS 3 was in the library, but it was very unpopular for a number of reasons I won't go into here. Atari DOS 2.0 and 2.5 where considered "Standard". Note- Atari DOS 2.5 came out after Atari DOS 3.