Obsidian

Obsidian is a Markdown-based note-taking app that stores everything as plain text files on your computer. No proprietary database, no cloud lock-in. You can open your notes in any editor, grep through them from a terminal, or write scripts against them. That's what makes it different from Notion or Evernote — you own your data.

The two features that matter most are wikilinks and backlinks. When you write Redis in a note about caching, that creates a connection. Over time these connections compound. You open a note and discover backlinks from things you'd forgotten about. The vault remembers relationships you don't.

See How I Use Obsidian for how I've set up my own vault around these ideas.