I owe a lot to flash cards. I'm not sure I would have ever gotten multiplication tables had my mom not used flash cards to help me study. I'm not sure how many people still use flash cards but there's no denying they help students memorize everything from vocabulary words to the table of elements.
Quizlet is an app that brings flash cards into the 21st century. Students and teachers have created and organized over 140 million sets of flash cards (according to the company) and share them with the community. It's searchable by subject or school, but you don't have to be enrolled in school to use it.
Quizlet has the old fashioned flash cards which display the question on one screen. A tap turns the card over for the answer. I tried it using a course designed to teach people Italian. Not only do the cards have the words but you can listen to how it is pronounced. You can go back and play the flash cards over and over again.
Quizlet also has match-games and practice tests. Students can create the study sets and share them with classmates while teachers are creating their own set for each class.
I found this app to be a much better for teaching that some of the other 'homework helper' apps which just give away the answers.
Quizlet is a free app for iPhones, iPads and Android devices but the free version does come with ads covering part of the screen. You can also use Quizlet on its website www.quizlet.com