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.
Laoshi - Learn new words with flashcards to master Chinese faster
Quizlet - Quizlet allows you to review and create flashcards for a variety of subjects, such as math and reading.
Ninchanese - Learn Chinese with Ninchanese and discover how addictive Chinese can be
AnkiDroid - Memorize anything with AnkiDroid!
YiChi - YiChi helps people Speak Mandarin Chinese