Meshtastic

TL;DR

An open-source mesh network protocol that lets you send text messages over long-range radio without needing a cell tower or a data plan.

Who is this actually for?

Outdoor enthusiasts, privacy nerds, and festival-goers who need to stay in touch where cell service is non-existent.

The Good

• Hardware is incredibly cheap; you can get started with a $25 ESP32 board and some LoRa antennas.
• Total privacy since it uses end-to-end encryption and doesn't rely on a central server or big tech infrastructure.

The Catch (Potential Downsides)

The bandwidth is extremely limited, so forget about sending photos or voice notes. It also requires a fair bit of tinkering with firmware and antennas, which will scare off anyone who just wants things to work out of the box.