MQTT (3)

• RabbitMQ: One broker to queue them all | RabbitMQ (rabbitmq.com) tool
  AMQP 1.0 and MQTT 5.0 broker for queues and streams; MPL-2.0 at no cost, paid Broadcom Tanzu support
  Commercial Support Message Broker #
• Eclipse Mosquitto (Eclipse Mosquitto) tool
  lightweight EPL/EDL MQTT 5.0 broker for IoT, plus C client library and pub/sub CLI clients
  Message Broker #
• MQTT - The Standard for IoT Messaging (mqtt.org) reference
  pub/sub IoT messaging protocol: three QoS levels, persistent sessions, small headers, TLS and OAuth auth
  Message Broker #