I find it interesting that here in Berlin (and other cities in Europe, mostly in Germany), we have this for many years - not just for protesters, but for anyone. However, it's not a smartphone app (the network predates smartphones), but a mesh network of WLAN access points. The name of this project is Freifunk: http://freifunk.net/en/
IIRC a number of the contributors to the downstream projects of Serval were some of the early contributors to freifunk.net.
My understanding is that freifunk was a pretty major testbed for peer-to-peer mesh network protocols in Linux, and it's that heritage that's made it into things like Serval and the Mesh Potato.
Whilst Serval has moved on to its own OSLR variant, its roots are firmly embedded in the B.A.T.M.A.N. protocol.
