memordo - Spaced repetition tool to help you retain more knowledge
Reflect App for Evernote - Remember what's important with flashcards
SmartCards+ - Spaced Repetition Software for iOS. Modern, powerful and easy to use.
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
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.