FreeRice 

For each word you get right, we donate 20 grains of rice to the United Nations World Food Program.

WARNING: This game may make you smarter. It may improve your speaking, writing, thinking, grades, job performance...

The rice is paid for by the advertisers whose names you see on the bottom of your vocabulary screen. This is regular advertising for these companies, but it is also something more. Through their advertising at FreeRice, these companies support both learning (free vocabulary for everyone) and reducing hunger (free rice for the hungry).