This looks like it would come in handy next time I get caught in a snowstorm: an emergency shelter that can be set up in 40 minutes. It's delivered in a bag which is ripped open and then has water added. The concrete is activated by soaking up the moisture, and the unit is inflated by a battery operated pump. In 12 hours, the whole thing is solid, and will withstand a bullet shot!
Obviously, not trully practical for hikers and campers; but it made me wonder, what kinds of emergency shelters (improvised or otherwise) have you come across?