Spaced repetition: questions are asked again only when you are about to forget (but have not forgotten!) the answer. This allows for better memorisation.
Leximnesia is an application that helps you learn vocabulary and other things through a game of questions/answers. Each time you answer a question, Leximnesia gives you the right answer and tries to compute the optimal time at which it will ask you the same question again, depending on whether your answer was correct or not (this is called spaced repetition).
If you don’t want to type your answers, just think of them and click the buttons “I know” or “I’m not sure”: Leximnesia will do as if you had typed respectively a right or a wrong answer. But what if you had thought of the wrong answer and clicked “I know”? Then you can click on “Cancel” and cancel the last move. It is as simple as this.
Start quiz". The direct URL to the web version is js.leximnesia.org. Feel free to click anywhere!
If you are a teacher, you may be interested in HotPotatoes, though it is not based on spaced repetition.