#notes A Zettelkasten is said to be a second brain. Through the linking of notes the system may surprise you in insightful ways. What is a zettelkasten? The word can be split into two ‘zettel’ and ‘kasten’. Zettel meaning a note and kasten simply box. So, a zettelkasten is a box of ideas. But what makes this box special/useful? Ideas behind zettelkasten Rather than writing notes down in categorized notebooks the notes should have a free-flowing category.