I had Firechat installed for a while during the
February 2017 protests in my country. Someone suggested using it because the cellphone lines in the area would get really crowded since a lot of people (hundreds of thousands to be more precise) would start calling, messaging, or even sharing stuff on social media all at once.
Orange and
Telekom had to bring mobile relays so that the networks would be decongested.
The idea of creating some mesh networks using people's devices as relays is quite nice and useful when stuff gets too crowded, but on the surface Firechat seems only another internet chat app. I found no way to make it establish somewhat of a mesh network or what it advertised. I found there was some sort of accesibility setting on my device (using Android 6.0) but I couldn't test it since the protests had tempered down by then and there was no risk of getting the lines congested.
You could also check
The Serval Mesh project if you are interested in this (if it is still up and running)