This book from 1908 by J. Kaiser seems like a fantastic instruction manual for how to use Obsidian, Logseq, Notion, Evernote, OneNote, and most other note taking tools for just about any application.
Tag: card index for business
Zettelkasten for Dogs.
Seen in the wild: An actively functioning card index (zettelkasten) used to manage a local dog grooming business.