www.freerice.com

I stumbled upon this website during my last student teaching placement.  This website is non profit and was created by the United Nations World Food Programme.  You visit this website and answer multiple choice questions arranged by school subject.  For each correct answer, ten grains of rice are donated to help end world hunger all over the world. This website is able to function because a sponsor's logo pops up for every questions, but I didn't find that it was distracting or annoying in any way.
My CT used www.freerice.com as a game at the end of a class.  Students were divided into two teams and took turns answering questions.  She kept track of points. This was a very basic use of the website, but it could also be used as a starting point or activating strategy to get students thinking about world hunger and humanitarian aid. They could do research into how non profit organizations work, and how they are funded. It could be useful for grade 7 S.S. when discussing NGO's and government funded organizations.  It would also be useful in a world issues class while studying world hunger.
You can also sign up for the website, and it will track your answers so you can see how much rice has been donated from your correct answers.  You can add students to your "classroom group" and track the entire class' progress. I could see this program being used the entire year, maybe to kill five or ten minutes at the end of a class. The bonus is that you can select your subject, and students answer progressively more difficult questions.  I would say it is a good "game" because students are still learning something while enjoying themselves.  Some kids will thrive on the competition of answering more questions correctly than their peers, but it doesn't have to be used in a competitive manner.
I don't really see any downside to the website, and I think it could be a useful tool in any classroom and for any subject! You and your students can feel good because you are doing something positive to end world hunger.
Seems like a win-win to me. Check it out!