MemoStack - MemoStack is a flashcard software that help you memorize more things with less effort. It works great for test preparation, language learning, and more.
Harken - Flashcard app using smart repetition to improve your memory
SpacedTime - Remember the important things in your life
Brainscape - Find, create, and study SMART FLASHCARDS on any device. DOUBLE your learning speed using the most effective study system on the planet. Keep all your content in sync across Brainscape's website and your Android devices.
FlashTabs - Flashcards in your new tab screen
memordo - Spaced repetition tool to help you retain more knowledge