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.

LingQ is a language learning platform built on the principle of comprehensible input. It provides a vast library of articles, podcasts, interviews, and books, often with accompanying audio. As users read and listen, they can instantly look up new words and save them as "LingQs" for later review with a built-in spaced repetition system. The app visually tracks vocabulary growth, allowing learners to choose content suited to their level. It's an excellent tool for intermediate to advanced learners looking to expand their vocabulary and improve comprehension through massive exposure to authentic material.