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.
Forvo - Forvo: the largest word pronunciation dictionary in the world, now with translations.
Quizlet - Quizlet allows you to review and create flashcards for a variety of subjects, such as math and reading.
Howjsay - Pronounce words correctly with the world’s largest English pronouncing dictionary.
Memrise - Learn a new language with games, humorous chatbots and over 30,000 native speaker videos.
Shtooka - The Shtooka Project is a multilingual database of audio recordings of words and sentences.