University of Southern California engineer Behrokh Khoshnevis and colleagues are developing a 3D printer for houses. Called Contour Crafting, the system spits out layers of concrete to build a structure from the bottom up. Caterpillar is sponsoring Khoshnevis's research. From the Contour Crafting page:
Contour Crafting technology has great potential for automating the construction of whole structures as well as sub-components. Using this process, a single house or a colony of houses, each with possibly a different design, may be automatically constructed in a single run, embedded in each house all the conduits for electrical, plumbing and air-conditioning.
The potential applications of this technology are far reaching including but not limited to applications in emergency, low-income, and commercial housing.
Our research also addresses the application of Contour Crafting in building habitats on other planets. Contour Crafting will most probably be one of the very few feasible approaches for building structures on other planets, such as the Moon and Mars, which are being targeted for human colonization before the end of the new century.
Contour Crafting (company page),