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.
Wordd - Quickly look up vocabulary, abbreviations, acronyms, slang
Reji - Improve your vocabulary hassle-free π
Yak Tack - remember. words.
Words For That - the reverse-Urban Dictionary of the internet
Synonymful - Improve your vocabulary and communicate like a pro.