MQTTnet is a high performance .NET library for MQTT based communication. It provides a MQTT client and a MQTT server (broker). The implementation is based on the documentation from http://mqtt.org/.
HiveMQ CE is a Java-based open source MQTT broker that fully supports MQTT 3.x and MQTT 5. It is the foundation of the HiveMQ Enterprise Connectivity and Messaging Platform
HiveMQ MQTT Client is an MQTT 5.0 and MQTT 3.1.1 compatible and feature-rich high-performance Java client library with different API flavours and backpressure support
Toolkit is a IoT protocol client CLI for IoT developer and learners. CoAP and MQTT protocol are currently supported. It supports colors, autocompletion, internationalization(chinese, english and german…) and multi-platforms
Whsnbg is a C implementation of a MQTT server (broker), a MQTT-SN gateway and simple MQTT rules engine designed for embedded platforms with small memory requirements.