http://freerice.com is an online quiz that helps you learn in many different subjects.
The difference is that here, the better you do, the more gets donated to the World Food Programme to help people around the world. It only costs you your time, but every time you get a question right, the equivalent of 10 grains of rice is donated.
How much rice can you get donated?
It takes about 20,000 grains of rice to feed 1 person for a day.