https://bitchat.free/
Something like this could be very cool if widely adapted, otherwise it is pretty limited to the Bluetooth signal between two phones. It could be useful for a bunch of people in a single compound who want private alternative to texting each other.
Meshtastic uses LoRa and can scale many miles. It takes outside hardware, but you can go back and forth from cell phone to a LoRa device. An off grid network can be as much as 2,800 miles wide and it can also tap into the internet or satellites to communicate globally if desired.
https://meshtastic.org/
I'm thinking of people using it during protests as in Hong Kong.
Evidently Modi isn't happy with it...
Government orders GitHub to remove Bluetooth-based chat app Bitchat over security concerns: Jack Dorsey - The Hindu
https://www.thehindu.com/news/national/government-orders-github-to-remove-bluetooth-based-chat-app-bitchat-over-security-concerns-jack-dorsey/article71262049.ece