Stacks is a language flashcard app that uses the FSRS spaced-repetition algorithm to help you remember vocabulary longer with less study. It's fast, minimal, offline-friendly, and ad-free.

Yes, Stacks works offline for creating and reviewing flashcards. When you're back online, your progress syncs automatically across devices.

Stacks is free and includes cross-device sync; the free plan lets you create up to 40 cards. Stacks Plus adds unlimited cards and automatic DeepL translations.

FSRS schedules each flashcard right before you're likely to forget it, so you review at the right time and retain more with less effort.

Stacks supports over 100 languages for card creation and study, so you can learn the language you actually care about.

Yes. Where available, Stacks automatically includes romanization for non-Latin scripts (for example Japanese, Arabic, Russian, and Hindi). There's no toggle.

Yes, automatic translations use DeepL and require an internet connection. This feature is available with Stacks Plus.

Yes, cross-device sync is included for all users. Study offline and your cards and progress will sync when you're back online.

Yes, sign in with Apple or Google is required for secure backup, cross-device sync, and subscription management.

On iOS, manage your Stacks subscription in Settings → Apple ID → Subscriptions; you can cancel or change your plan anytime.

Install Stacks on your new device and sign in with the same account; your synced cards and progress will return automatically.

Stacks has no ads and doesn't sell your data. We store only what's needed to run sync and subscriptions. See the Privacy Policy for details.

Stacks is focused on iOS.

For help with Stacks, email support@thestacksapp.com.

Yes, with Stacks Plus you can adjust FSRS request-retention to match your pace, and your schedule updates accordingly.

Suggest new features via the in-app feedback form. We're actively listening to requests.

No, Stacks is ad-free so you can focus without distractions.