Synonymful - Improve your vocabulary and communicate like a pro.
Duolingo - Duolingo is a free language learning app for iOS, Windows and Android devices. The app makes learning a new language fun by breaking learning into small lessons where you can earn points and move up through the levels. Read more about Duolingo.
Reji - Improve your vocabulary hassle-free 📚
Zorbi - Spaced-Repetition Flashcards - Other tools are built by boomers, Zorbi is built by students.
BurningVocabulary - Touch and highlight YouTube & Netflix subtitles
Mochi - Write notes and flashcards with Markdown and study them with spaced repetition.