"For each answer you get right, we donate 10 grains of rice through the World Food Programme to help end hunger"
FreeRice is one of the most ingenious, easy, and helpful sites I have seen on the internet in quite a while (if not in my entire time on it!). It donates many, many billions of grains of rice to the hungry people in third-world countries, where local inhabitants would not normally be able to feed themselves. It also doubles as an excellent device for learning or practicing such subjects as English vocabulary, foreign languages, geography, and more.
The idea at FreeRice is very simple -- in fact, it is so simple, you might not believe I am being 100% genuine until you try it out for yourself. Essentially, when you go to the site, you will immediately be presented with a question; answer it correct, and you will instantly be told that you have donated 10 grains of rice.
Answer as many questions as you want on any subject you want (you can click "Change Subjects" at the top right corner of the question box or the "Subjects" tab at the very top to change subjects) and for each correct answer, the site will donate 10 grains of rice instantly, guaranteed.
How can they do it? Well, this is where the ingenuity comes in (and for this, I think the creator, John Breen, deserves a medal or something!): each time you get a question, a banner appears at the bottom of the screen. This banner is not obtrusive at all (in fact, it is quite out of the way), but the advertisers pay for each time their banner is viewed. The current owners of the FreeRice site (the World Food Programme of the U.N.) use all of the money earned by advertising to pay for the rice.
Just by clicking the correct answer to a question, and perhaps even learning something, you can feed children and families all around the world! The World Food Programme says that 20,000 grains of rice provide enough caloric intake to sustain an adult for one day. That means it takes 100 people less than 2 minutes of consistently answering questions at a normal speed to feed an adult for the whole day!
The site also has a free FreeRice toolbar that's quick and easy to download. Once downloaded, use the search bar as you normally would your default search bar. For every 5 searches you do, FreeRice will donate 2,500 grains of rice, up to 5,000 grains per day. Search naturally, though; apparently "fake searches" to simply raise the rice donations will result in disabling of your rice donations for using the toolbar.
It is absolutely free, it is incredibly simple, and it is a really great thing to do. If you happen have some spare time, or if you are feeling a bit generous, go on there and do some good for your world, at FreeRice.