From Wikipedia:

MeshCore is an open-source mesh networking protocol and software platform designed for off-grid, low-power text communication using LoRa (Long Range) radio technology. The system enables decentralized, multi-hop wireless messaging without reliance on cellular networks or internet infrastructure.

Use cases include emergency and disaster communications, outdoor and remote activities, [...] and experimental and educational deployments of low-power mesh networking.

[It] is designed to [...] operate in unlicensed ISM frequency bands such as 868 MHz and 915 MHz, depending on regional regulations.

The basic idea is that you get a small companion device that you pair to your cell phone via bluetooth, and via that device, you can text others or post public messages using the 915 MHz band, all without a special license.

• Get a companion device like the Wio Tracker L1 Pro from seeed studio or from Robot Shop
• Flash the device with the latest Meshcore Firmware (using a chromium browser).
• Install the Meshcore app on your phone. (Android, iOS, Web App, NodeJS, Python)
• Pair the device with your phone.
• Turn off Auto-Add Contacts
• Use “Flood” login when at a new location.

• Install a repeater like the SenseCAP Solar Node P1-Pro from seeed studio or RobotShop
• Use an antenna like this one, this one or one of these.
• Install sensors.

• Official MeshCore Node map
• Community generated map
• MeshCore Analyser
• Path Profiler

• Official MeshCore Website and Github
• Youtube Presentation by Liam Cottle
• Scott Baker's Website
• Salish Mesh Website
• Forum
• MeshCore vs Meshtastic