One of the UN World Food Programme's most successful efforts, FreeRice.com awards 10 grains of rice to the hungry for every vocabulary question visitors answer correctly. As well as being for a good cause, the game is surprisingly addictive. In addition to testing the limits of your linguistic lexicon, you can also try your hand at identifying paintings, chemical symbols, flags of the world, etc. Since the site's inception,
visitors have collectively donated over 93 billion grains of rice. That's a lot of rice!