The Zettelkasten method

The Zettelkasten method is a knowledge management system developed by German social scientist Niklas Luhmann. Translated simply as "slip box", the concept behind Zettelkasten is to create an archive of notes where each individual note contains one single idea as concisely as possible and links to all other related notes.

By linking individual notes based on the ideas captured within them instead of grouping them by arbitrary categories, it's possible to build a hugely powerful "thinking tool" to support your creative work.