reticulum, in theory, can go over any medium. Radio or internet, whichever is present.

you use it to access the internet, but the point is if the internet access is disabled you still have a local network for p2p communication across the city. also multiple people/hubs in the network can provide provide internet access over different ISPs providing resilience if some ISPs go down, but not all of them.

freifunk in germany and funkfeuer in austria do the same thing.