NYU's ITP Winter Show allowed their students to display their new incredible inventions. My favourite and the one I can believe would work in the real world is called TweetGrass and it aims to encourage communities to take better care of the environment. Here is how it works:
Users do a good deed for the environment, let everyone know about it by tweeting at @tweetgrassnyu and then "these tweets are transformed into clouds on a monitor, when it gets cloudy enough, the digital to real world transformation happens and the community wheat grass is watered."
image from tweetgrass.worldpress.com
I truly do believe that if a large enough organisation backed this project up it would be a fantastic way to encourage everyone to take care of the environment. People can share what they are doing to help and together as a community everyone helps to "water the planet".
Progress of this project can be viewed at http://www.tweetgrass.worldpress.com/