Eclipse Mosquitto MQTT Broker

Eclipse Mosquitto is an open-source MQTT message broker that implements the MQTT protocol versions 5.0, 3.1.1, and 3.1, providing lightweight publish-subscribe messaging. Originally developed by Roger Light in 2009, Mosquitto has been an Eclipse Foundation project since 2013 and is one of the most widely deployed MQTT brokers for IoT applications. Key features: full MQTT 5.0 support including shared subscriptions, session expiry, message expiry, topic aliases, user properties, and content type. Supports MQTT 5.0, 3.1.1, and legacy 3.1, plus MQTT over WebSockets for browser-based clients. Written in C with minimal dependencies, consuming very little CPU and memory, suitable for Raspberry Pi and embedded devices. Full TLS support for encrypted client-broker communication with certificate-based authentication and PSK ciphersuites. Configurable authentication via password files, pluggable authentication plugins, and external authentication services. Topic-based access control lists (ACLs) for fine-grained publish and subscribe permissions per client. Broker-to-bridge connections for distributing messages across multiple brokers creating scalable MQTT networks. Automatic saving of messages and subscriptions to disk enabling state recovery after broker restart. Native MQTT over WebSocket support for real-time web applications. Built-in monitoring topics publishing broker statistics including connection counts and message rates. Official Docker images for containerized deployment. Command-line clients (mosquitto_pub and mosquitto_sub) for publishing and subscribing from terminal scripts.