From the about page:
“Block by Block” is an innovative partnership between the United Nations Human Settlements Programme (UN-Habitat), the UN agency promoting sustainable towns and cities, and Mojang, the makers of Minecraft.
Block by Block involves young people in the planning of urban public spaces. Minecraft has turned out to be the perfect tool to facilitate this process.
The four-year partnership will support UN-Habitat’s Sustainable Urban Development Network to upgrade 300 public spaces by 2016. The first pilot project in Kibera, one of Nairobi’s informal settlements is already underway.