Zettelkasten is German for ‘slip-box’, IE, a box with slips of paper in it. You keep everything on a bunch of note cards. Niklas Luhmann developed the system to take notes on his reading. He went on to be an incredibly prolific social scientist. It is hard to know whether his productivity was tied to Zettelkasten, but, others have reported large productivity boosts from the technique as well.
Luhmann used paper for his slip-box, right now there are a lot of great softwares that we can use for this. I personally use Obsidian. I am in love with it and I think this is the best for my current workflow.
To read more on Zettelkasten: https://zettelkasten.de
These notes are still a work in progress. If you have comments or feedback you can reach me out on Twitter or send me an email.