FireChat uses Bluetooth and peer-to-peer wifi to enable people to message each other directly, phone-to-phone. When the power goes out, cell towers will last only as long as their backup batteries work, which is not long at all. Because FireChat doesn't rely on cell towers or the Internet, FireChat makes it possible to communicate even during the most extreme disaster. Imagine that: cell phone messaging without a cellular network or the Internet.
Previously, FireChat's range was limited to 70 meters. With FireChat's recent update your message hops from FireChat user to FireChat user until it reaches its destination. It may take a while for your message to reach your family, friends, or coworkers, but it eventually will.
Free iOS and Android FireChat apps can be found at http://opengarden.com/firechat.