ubus - User space inter process communication that adheres to the Unix philosophy.
MQTTBox - MQTTBox enables to create MQTT clients to publish or subscript topics, create MQTT virtual device...
RabbitMQ - RabbitMQ is an open source message broker software.
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
nanomsg - nanomsg is a socket library that provides several common communication patterns.
MQTT Explorer - An all-round MQTT client that provides a structured topic overview