Summary
This site can be an excellent companion to any web-based endeavor to learn a language, especially since the cards are stored online and you can be traveling and using random computers to access your study cards.
With this site you can quickly and easily create your own flashcard tests for anything you choose to study: vocabulary, grammar concepts, phrases... the cool thing is it's up to you.
Also at your disposition is a huge database of public flashcard packs to choose from, covering a large number of languages.