Spaced Repetition & Flashcards
Anki, RemNote, Mochi, Quizlet — long-term retention via FSRS / SM-2 algorithms.
Spaced repetition is the closest thing to a free lunch in learning: review cards just before you forget them, retain for life. The 2024-26 story is FSRS — a modern, open-source algorithm that beats SuperMemo's classic SM-2 by a wide margin and is now baked into Anki. For class quizzes (short-loop) see Quizzes & Assessment; for note-taking that pairs with cards see Self-hosted Notes & Wikis.
The dominant FOSS pick
- ★ ★ Anki — AGPL desktop + AGPL AnkiDroid (Android, free) + AGPL AnkiWeb (free sync). AnkiMobile on iOS is paid (~$25 one-time) — the proceeds fund development of the entire free ecosystem; the desktop is fully free forever and includes everything iOS does. Hand-edit cards in HTML/CSS/JS; massive shared-deck library; 700k+ AnkiDroid users in 2026.
- ★ FSRS algorithm (Free Spaced Repetition Scheduler) — replaced Anki's old SM-2 default in Anki 23.10 (2023) and is now the recommended scheduler. Roughly 20-40% fewer reviews for the same retention. Open source; ports for other tools.
- AnkiPro — free Anki-compatible mobile app; not affiliated with Anki team; mixed feelings in the community (uses the brand). The official AnkiDroid is the safe Android pick.
Hosted modern alternatives
- ★ RemNote — free + paid; outliner-style notes with built-in spaced repetition; cards inline in notes. Web + desktop + mobile.
- Mochi — paid + free tier; markdown-flavoured; nice card templates; FSRS supported.
- Supermemo (SuperMemo World) — the original 1985 spaced-repetition app + algorithm; paid; SM-18 is the latest scheduler (FSRS aims to match its quality with a smaller code-base).
- Quizlet — paid + free; popular in schools; "Learn" mode is closer to spaced repetition than pure flashcards. Has been criticised for selling Quizlet Plus features that lock the better algorithms.
- Brainscape — paid; Confidence-Based Repetition (CBR) variant.
- Memrise — paid + free; gamified; mostly languages.
- Cram.com, StudyBlue, GoConqr — older free alternatives.
Open / pluggable
- Obsidian Spaced Repetition plugin — free; turns Obsidian notes into cards.
- Logseq Cards — free; built into Logseq.
- rsrs (Rust SRS) — small CLI for reviewing cards from a JSON file.
- fsrs-rs / py-fsrs — open source FSRS implementations to embed in your own app.
- Mnemosyne — older FOSS desktop SRS; predates Anki in some ways.
Card creation tools
- Anki AI / smart card add-ons — generate cards from PDFs, articles, lecture transcripts.
- Wozlearn, JPDB — Japanese-specific.
- Migaku — paid; language-immersion-flavoured Anki front-end.
- Vocabulary.com, Clozemaster — sentence-level cloze; good for languages.
Sunset / dead
- Tinycards (Duolingo) — sunset 2020.
- StudyStack — alive but stagnant.
- Brainscape free tier — heavily restricted in 2024.
Pick this if…
- Default, best, FOSS, longest-running: Anki desktop + AnkiDroid + AnkiWeb sync.
- iOS user, willing to pay $25 once to fund the project: AnkiMobile.
- Markdown / outliner workflow: RemNote or Mochi.
- Notes-first, cards as a side-effect: Obsidian SR plugin or Logseq Cards.
- Schools / casual classroom use: Quizlet.
- Language immersion: Migaku or Anki + JPDB.
- You're building your own SRS app: the FSRS algorithm libraries.