Minecraft developer Mojang is teaming up with the United Nations for a project called Block by Block, which aims to involve people—especially youth—in the planning process of urban areas by giving them the opportunity to show planners and decision makers a concept of how they'd like to see the cities of the future.
The project is being developed in partnership with UN-Habitat's Sustainable Urban Development Network to upgrade 300 public spaces by 2016 in developing countries. The pilot project will take place in Kibera, an informal settlement currently in development in Nairobi, Kenya. Here's an idea of what they'd like to see:

Being the good guys that they are, Mojang will be the main financial sponsor for Block by Block, and the studio intends to work very closely with the United Nations to help them reach their goals.
The Block by Block project follows Mojang's success with the Svensk Byggtjänst (Swedish Building Services) which involved people in the reconstruction of their own neighborhoods within Minecraft. You can read about that other project here.