Researchers at MIT's Self Assembly Lab have developed a new technique for 3D Printing which they call "4D Printing". It's 3D printing of objects designed to change their shape after printing.
By exposing the printed object to a different external environment - think light, water, pressure, etc., specially designed joints in the object react and cause the object to change shape.
Using equipment from their partner, Stratasys, MIT was able to produce simple shape reorganizations at a small scale. In the video you can see how a formerly straight tube changes shape when exposed to a water environment.
The concept is good, particularly if it can be scaled up. Imagine 4D printed materials that can be efficiently stored for shipment and then take their final shape upon delivery. Construction materials, such as pre-fab walls or windows frames could benefit from this approach.