Quizlet is a website that lets you create flashcard type quizzes, and then quizzes you on them. It maintains statistics on what you've answered correctly, and can test you in a variety of ways, such as how many can you get correct in a fixed time, 

Requires creating an account, you can create a profile on the site, or use a Google or Facebook account to authenticate.

A basic account is free, letting you create text based quizzes. The site accepts Unicode input. A $15 per year subscription (Quizlet Plus) lets you record audio and upload pictures, a $25 subscription (Quizlet Teacher) allows audio and pictures, lets you create quizzes for your students, and see how they do on them. Subscribing also hides the ads on the site.

Besides the web interface, there are apps for iOS and Android. Search for "quizlet" in the app store. The apps reportedly download content, so that presumably once you have installed the app and synched with the website, you can use the app without being online.