RabbitMQ - RabbitMQ is an open source message broker software.
CloudMQTT - CloudMQTT implements MQ Telemetry Transport protocol for carrying out messaging using a publish/subscribe message queueing model.
EMQX Enterprise - Self-managed scalable and reliable MQTT messaging platform, an all-in-one distributed MQTT broker with multiple protocol gateways and a powerful built-in SQL-based IoT rule engine.
HiveMQ - HiveMQ is the MQTT based messaging platform for fast, efficient and reliable data movement to and from connected IoT devices and enterprise systems
Firebase Cloud Messaging - Firebase Cloud Messaging (FCM) is a cross-platform messaging solution that lets you reliably send messages at no cost.
EMQX - EMQX is an open source MQTT 5.0 broker for mission-critical IoT scenarios, massively scalable and highly available clustering, running anywhere from edge to cloud.