Wikilinks
The double-bracket link that turns a pile of notes into a network.
zettelkastenmarkdown
A wikilink looks like [[note-slug]]. That's it. Wrap a slug in double brackets and it becomes a path between two ideas.
The magic isn't the syntax, it's what it encourages: you link as you write, so the structure of your thinking emerges instead of being planned. Over time the links matter more than the notes.
This whole This Digital Garden is wired together with them. Every [[...]] you click is one. Backlinks (who points at this note) come for free once you parse them all - see Zettelkasten.