Meshtastic (and Meshcore) are common names for digital communication protocols, using the LoRa radio frequencies. This bandwidth is currently set aside for Internet of Things features. But it is now also being used with these protocols to send text communication in digital packets.

These protocols make different trade-offs in usage, but both Meshtastic and Meshcore offer both open and encrypted text comms over mesh networked devices. Mesh networks allow for ad hoc networks to be created by devices that are set up to be able to talk to each other with pre-shared keys. Some places to go read about this from people that know more about it:

• Meshtastic - general Meshtastic protocol orientation
• Network Site Planner - how many nodes would you need to cover an area?
• Map Tile Downloads - getting local maps onto a node
• Bostonme.sh - existing Boston-ish mesh network
• Meshcore - another LoRa protocol
• Rokland is a vendor with a range of devices