Anki is a powerful, open-source flashcard program renowned for its effective spaced repetition system (SRS). It isn't a language course itself, but a highly effective tool for memorizing vocabulary, phrases, or grammar rules that you input yourself or download from shared user-created decks. Its high degree of customization allows for rich cards with audio, images, and cloze deletions. While its interface can be unintuitive for new users, its effectiveness for long-term retention is largely considered unparalleled for dedicated learners.

LingoDeer is often seen as a more structured alternative to apps like Duolingo. It provides a well-organized curriculum with detailed grammar explanations at the beginning of each lesson, which is especially helpful for understanding complex languages. The app is highly regarded for its courses in Japanese, Korean, and Chinese. While its lesson format can feel repetitive, it builds a solid foundation in grammar and vocabulary for beginner to intermediate learners.