Ripple Messenger

This is intended for groups which are out of cell coverage, eg. camping/hiking, and wish to use SMS-like communications.

This app is used in conjunction with a DIY LoRa radio module. Full instructions on how to assemble these are here: https://www.instructables.com/id/LoRa-Mesh-Radio

-Or here-

https://www.hackster.io/scottpowell69/ttgo-lora-mesh-chat-device-37913c

The radios use ECC encryption, so your conversations are completely safe from prying eyes. You can also easily send your GPS location as part of your conversation, and recipient can tap to see where you are on Google maps.