Meshtastic is a open source mesh network protocol and software for small low power radio devices that is not depend on internet, mobile network or any other infrastructure. You can use it to send text messages, position updates, telemetry (temperature, humidity, etc.). It's a fun hobby to learn about radios, antennas, networks, and find other same minded people.
As the name "mesh" indicates, the radios create meshing network where each radio can communicate with each other. This way the network can grow large and messages can be sent to longer distances than in radio-to-radio communication.
Text Source & Credits: https://meshpirkanmaa.org
OH1MAC Meshtastic nodes are based on two configurations. A Basestation with a fixed location and settings to serve as a client node broadcasting (thus relaying) all LoRa traffic, and a battery-powered Mobile node that is carried along when moving around the city. More details ...