Free Rice!!
Improve your vocabulary while earning rice for the poor. 20 grains of rice are given for every word you know.
You pay nothing, you learn new words. The system automatically adjusts to your vocabulary level.
The advertising space on the freerice.com page pays for the rice - the longer you spend on the site and the more people who visit the site ie. the more words people get right - the more money is given for rice.
What a brilliant idea.