FreeRice is a clever website that donates 10 grams of rice every time you correctly answer an english word defintion. So in principle, you expand your english vocabulary and feed the hungray at the same time.
Perspective: I think “Not for profits” are succeeding in leveraging the demand to help global issues, by both producing engaging sites. The combination of these reasons produce a powerful incentive for people to spread the site through word of mouth / mouse to others.
via CTV.ca
