FireChat is a messaging tool that, unlike all of the other apps that are available for Android devices, does not need an Internet connection in order to send and receive messages. This is due to the OpenGarden network technology, which allows you to communicate with other devices nearby even if you don't have an Internet connection.
The only problem with this is that it only allows you to have conversations in public chat rooms. In other words, FireChat users cannot have private conversations with their friends. Instead, you will have to talk in those chat rooms, with all of the problems that come with them.
Another big advantage of FireChat compared to all of the other messenger apps is that it doesn't ask you for any account information. You don't have to register using your phone number, your Facebook account, or anything else. You just have to enter your name and you're in.
FireChat is a curious messaging app that is more of a tool to satisfy your curiosity and see what people around you are talking about, rather than a traditional instant messaging service.