Quizlet

Quizlet.com is a free website which enables teachers and students to create digital flash cards. That’s not where the magic stops, however. Quizlet can automatically generate interactive games and even tests of the material you enter into it. Five or ten minutes of typing (or pasting!) up front can yield literally hours’ worth of automatically-assessed activities inside and outside of the classroom, on computers, smartphones, tablets, and even pencil-and-paper printed exercises.

I've prepared a quiz for my 2nd grade students to learn colours in English. It's a very useful app to attract students', especially elementary students, attention and make them focus on the lesson. 

Here you can have a look at my quiz!