emqtt is described as '- erlang mqtt broker'. There are seven alternatives to emqtt for a variety of platforms, including Linux, Mac, Windows, Self-Hosted solutions and Amazon Web Services. The best alternative is mosquitto, which is both free and Open Source. Other great apps like emqtt are MQTTBox (Free), CrystalMQ (Paid), HiveMQ (Free Personal) and VerneMQ (Free, Open Source).
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 from low power single board computers to full servers.
VerneMQ is an open source, high-performance, clusterable MQTT broker. It scales horizontally and vertically on commodity hardware to support a high number of concurrent publishers and consumers while maintaining low latency and fault tolerance.