Busuu

Busuu's killer feature is its community correction system: you submit writing and speaking exercises that get reviewed by native speakers of your target language, and you review theirs in return. It's like having a free language exchange partner built into the app. Busuu offers courses in 14 languages aligned to the CEFR framework (A1 to B2), and a McGill University study found that 22 hours of Busuu study equals one college semester. Acquired by Chegg in 2022 for $436 million.