Back in my day, we had The Hunger Site, which allowed you to give free rice to people in need. Free Rice does this one better. Not only can you give... free rice, you can build your vocabulary.

Or, if you're like me, you can use it to prove just how big your vocabulary is. Mostly I hover around 37, but my highest is 42, and so far I've give over 3,000 grains. See if you can do better. (My other favorite game is seeing how many words I know from D&D).