Sometimes people here make posts about minimalistic services that do the same work but with the less amounts of code.

I want to change discussion a little. What about services that have a goal to work in BAD conditions. Like services that let you communicate (privately) even if you have a very unstable connectivity. For example in case of massive blackouts in some area (like in my country today or after some natural disaster).

I really don't care if my messenger is few megabytes bigger when it can work even in few KB/s EDGE network. I don't also care if it is some Electron webshit or works only in command line. I want it to survive even a global catastrophe.

For this reason I don't suggest Matrix usage. I can never be sure if other side will see my message sent via disappearing mobile network.

Do you know this type of services? Messengers, fedi clients, etc..
Boosts appreciated.