Design principles

Browsing a file tree feels productive, but it's passive. You're recognizing information, not retrieving it. Real retention comes from active recall: the effort of pulling something from memory.

That's why S4 doesn't have a file tree. Navigation happens through the quick switcher and wikilinks, which require you to remember what you're looking for, and what you put in S4. Every navigation is a small act of recall.

S4 naturally reminds you that your notes exist through spaced repetition and semantic similarity, so nothing quietly disappears.

Most flashcard systems force you to maintain notes and cards separately. Content gets duplicated, then drifts out of sync. You update one but forget the other.

In S4, flashcards are embedded directly in your notes. Update the note, the card updates. There's no copying, no syncing, no maintenance overhead. Your notes are the source of truth.

Folders imply neat boundaries between concepts. But knowledge is interconnected. Ideas link to ideas, which link to others. Forcing this into a tree structure obscures the real relationships.

S4 uses bidirectional links to let concepts connect naturally. The resulting graph reflects how your knowledge actually fits together, and it informs how the spaced repetition algorithm schedules your reviews.

Beyond explicit links, S4 understands what your notes are about. Embeddings capture the meaning of your content and are stored locally in SQLite, right alongside your notes. This powers search by concept and surfaces related notes you might have forgotten.

This isn't a bolt-on feature. Semantic search and similar notes are core to how S4 helps you navigate a growing knowledge base. The more you write, the more useful it becomes.

Notes are plain markdown. Review data and embeddings live in SQLite on your machine. The app works fully offline. Cloud sync is available but optional.

If you leave, your data leaves with you. No export required.