SmartCards+ - Spaced Repetition Software for iOS. Modern, powerful and easy to use.
Word of the Day - Learn one new word, every day
Zorbi - Spaced-Repetition Flashcards - Other tools are built by boomers, Zorbi is built by students.
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.
Harken - Flashcard app using smart repetition to improve your memory
Wordd - Quickly look up vocabulary, abbreviations, acronyms, slang