Eclipse Mosquitto

A compact MQTT broker that accepts publish and subscribe connections from sensors, devices, and scripts over TCP, WebSocket, or TLS. It speaks MQTT 3.1.1 and MQTT 5, supports all three quality of service levels, retained messages, persistent sessions, last will messages, and per-client access lists, and can bridge topics to other brokers.

Home automation users point it at temperature probes, doorbells, and badges, while developers use it to carry telemetry between scripts and applications.

Self-hosting it self-hosting means device traffic never leaves your premises, there is no broker fee based on message volume, and the broker can be snapshotted and restored with the rest of your stack.