The original 43 folders.

43 Folders: "I was recently skimming through my beloved old 1934 edition of Progressive Indexing and Filing, which I inherited at a young age from my grandmother—probably my first piece of productivity porn (the book, not my grandmother.) On page 85, I stumbled across a delightful little gem. Apparently, not only did the David not invent the tickler file (news to me), but it’s been around since at least 1934."