RabbitMQ - RabbitMQ is an open source message broker software.
MQTTBox - MQTTBox enables to create MQTT clients to publish or subscript topics, create MQTT virtual device...
Apache Kafka - Apache Kafka is an open-source message broker project developed by the Apache Software Foundation written in Scala.
mosquitto - Eclipse Mosquitto is an open source (EPL/EDL licensed) message broker that implements the MQTT protocol versions 5.0, 3.1.1 and 3.1. Mosquitto is lightweight and is suitable for use on all devices
Resque - Resque is a Redis-backed Ruby library for creating background jobs, placing them on multiple queues, and processing them later.
MQTT Explorer - An all-round MQTT client that provides a structured topic overview