Quizlet is an online and mobile (free Android and iOS apps available) for creating and studying flashcards. I've written about Quizlet many times over the years as the service has steadily released enhancements. The latest update that I've noticed is the option to create folders for your flashcards. Each of your folders can have subfolders or subsets of flashcards. Within each of your folders you can search for and sort individual flashcards. You can review your flashcards in a folder by simply selecting one of the six review modes that Quizlet offers.
Quizlet can be made public. Likewise, all of the folders that you create can be made public. Making a folder public allows you to quickly share your flashcards with others. The flipside of that is that because folders are public it is easy to quickly assemble a set of flashcards for yourself.
Applications for Education
One of the aspects of Quizlet that I like is the "speller" review mode. Speller mode plays words for you that you then have to type correctly into the space provided. If you misspell the word that is read to you, Quizlet will show you your errors.