Vocabulary Miner - Flashcard app with offline learning, spaced repetition, no ads, export & import, statistics...
Anki - Anki is a program which makes remembering things easy. Because it's a lot more efficient than traditional study methods, you can either greatly decrease your time spent studying, or greatly increase the amount you learn.
Grammarian PRO2 - Like an English teacher looking over your shoulder
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.
Mondly - Learn 33 languages in 500 bite-size lessons and 14 conversational modules.
Drops - Visual language learning.