HiveMQ - HiveMQ is the MQTT based messaging platform for fast, efficient and reliable data movement to and from connected IoT devices and enterprise systems
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
VerneMQ - VerneMQ is an open source, high-performance, clusterable MQTT broker.
MQTT Explorer - An all-round MQTT client that provides a structured topic overview
RabbitMQ - RabbitMQ is an open source message broker software.
MQTT.fx - MQTT.fx is a MQTT Client written in Java based on Eclipse Paho.