In his blog, Andy Matuschak coined a concept of Evergreen notes - note-taking approach, aimed to maintain the information structured, and promote insight. It is based on a "Zettelkasten" method, originally invented by Niklas Luhmann, and described in a Taking Smart Notes by Sönke Ahrens.

In the Zettelkasten system, notes are store as atomic peace's of information, connected with links. The original version was a simple box with cards, physically sorted:

That system allowed linking and structuring information in various ways, long before databases were invented.

Evergreen notes take this idea further, leveraging note-taking software such as Obsidian, adding the following adjustments to the predecessor:

• Network over hierarchy. Instead of structuring notes hieratically, splitting a complex topic into smaller subcategories, Evergreen Notes are promoting associative taxonomy, when various concepts might be connected with other concepts forming graph-like structure.
• Inbox. Similarly to GTD, new information should be placed into an inbox, for further processing. The implementation of the inbox might be up to the user, for example, I'm using Todoist as my general-purpose inbox for both tasks and notes.
• Spaced repetition. A process of revisiting existing information should be set up. For Obsidian users there are multiple plugins that could help with that: core Random Note, and community, flash-card based Spaced Repetition are worth mentioning.
• Map Of Content (MOC). MOCs allow connecting various notes in a single place using links. This way, you can define some topic that you're interested in.

This structure allows maintaining a quiet impressive amount of knowledge, for example here is the knowledge graph of CEO of Obsidian Steph Ango(each dot represents a note):