[thescriptkiddie]

Serval actually does this with WiFi mesh networking.

http://www.servalproject.org/

[SigmundA]

Wifi mesh seems obvious but at 2.4ghz or 5ghz too limited in range.

I was thinking 150Mhz~ MURS like Gotenna for a few miles range.

[thescriptkiddie]

They have a "Mesh Extender" which uses 900 MHz ISM band radios for ~4 km range, and can be connected to an external HF radio if you have a HAM license. It even implements store-and-forward so you can send messages to people who are wandering in and out of range.