Please check out Freerice.com. You demonstrate your vocabulary prowess by correctly defining words (multiple choice) and Freerice donates grains of rice to those in need based on your correct answers. You clear your head, exercise your mind and others eat. Sounds like a fine arrangement to me. I've made it vocabulary level 45 before beginning to make mistakes.
I learned of Free Rice via Michael Leddy's very excellent blog, Orange Crate Art. Visit to read his writing and gain his perspective on the world.