Students feed the hungry and reinforce vocabulary and subject area knowledge at www.freerice.com. This can be used simply to track student participation and practice, or it can be used as an instrument for gathering data for classroom analysis.
How many people did our class feed this month? For how many meals? How many grains/correct answers/days would it take to feed X people?
My students love to use the site and ask to do it when they've finished all other assignments in class.