Tinycards is a flash card app from the people who make Duolingo. You can use Tinycards to learn and practice new English vocabulary. It is available on their website, and there is an app for iPhone/iPad (no app yet for Android). After you create a free account, and sign in with your username and password – you can practice with many sets of words, or you can make your own set to practice. Search for ESL, and they will give you many choices.