"The next time you're at a crowded place unable to send a message because of a congested network or poor signal, hold off on tearing out your hair. FireChat is a messaging app that lets you chat with others without a connection -- Internet or cell.

Thanks to an iOS 7 feature called Multipeer Connectivity Framework (MCF), the app tethers you to devices around you and sends messages directly via Bluetooth and Wi-Fi Direct."
http://news.yahoo.com/hidden-ios-7-feature-lets-152804496.html