Use cases would be regions where wifi is unreliable, on road trips or flights, etc.
I remember some paid apps from years ago, but I imagine there should be good Foss options too
Berty is being developed, and might have some promise.
Not sure what you mean with « mesh network » (I’m not native English) but Telegram is quite cool. It use a small internet debit, as a good native app for phone or pc, file transfer of multiple gb is possible (even more with the paid version), groups and subgroups, …
I’m not sure if that’s the right term, but basically services that don’t require a connection to the wider internet. The post body goes into it a bit more
I use signal day to day, but it would be nice to know about options for a local mesh network before I actually need it.
Check out secure scuttlebutt. I think there is even a phone app for it now. It was designed by a guy living on a boat with intermittent network access which is similar to the use case you describe.
There are social networking apps: Planetary and Manyverse.
Planetary is moving to nostr: