Ganked from noah_brand...
Free Rice allows you to test your vocab skills and give away free rice.
For every right answer, 10 grains of rice are donated to combat world hunger.
I don't do well with the language side of things but I was able to keep my vocab skill between 38-42. After about 30, I am guessing at about half of the ones I get right. Of the ones I know it is more because I have see the question word and the answer word in the same context, not that I know specifically what they each mean. But that still means that my vocab is doing pretty well considering how poor my English skills are (I am a pervy Math fancier after all).