Today’s post is not about development per se as much as a “down the memory lane” kind of thing. Back in the 90s, my friends and I used to like our little “Atari ST vs Amiga 500” rivalry. It was more like an amicable rivalry as both systems had their strength. On the Amiga 500 side, one thing I still remember decades later as IMHo the “quintessential” tool on Amiga was Directory Opus, especially version 4. This screenshot summarizes it well:

DOpus 4 on Amiga 500. [Source]

There’s a nice history of Directory Opus here that makes a great read:
https://amiga.abime.net/articles/amiga-lore/directory-opus 

There were a lot of good tools on the Atari ST, yet the simple and efficient UI of DOpus 4 was and is still something I enjoyed -- extremely compact, extremely contrasted, efficient to use.

A decade earlier, I was happily coding on Apple ][. The Apple ][e used DOS 3.3 and I switched to ProDOS for all my floppies on the Apple //c:

ProDOS [The same image is provided by source as well as source]

One thing I have fond memories of is actually manipulating the filesystem structure at the byte level with a “nibble” editor. Back then I severely lacked any kind of official OS documentation. That's something I continued doing on the Atari ST itself -- which was even easier as GEMDOS used a FAT12 filesystem which was very easy to comprehend at the binary level. With just a byte editor capable of dumping the raw content of a floppy, it was possible to quickly make sense of the structure and figure them out by trial and error because these just made sense.