There are 2 repositories under mqtt5 topic.
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
The fully compliant, embeddable high-performance Go MQTT v5 server for IoT, smarthome, and pubsub
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
A modern graphical MQTT client using the HiveMQ client library. MQTT is a messaging protocol widely used in the IoT world. CorreoMQTT provides a UI to send and receive messages. It is able to handle multiple connections at the same time.
MQTT Proxy allows MQTT clients to send messages to other messaging systems
Open source Extension SDK for the HiveMQ Enterprise MQTT broker that you can use to extend the broker with custom functionality and integrate the broker with other external systems
Official Docker Images for the Enterprise MQTT Broker HiveMQ
OSGi Messaging Specification RFC 246 and compliant MQTT 5.0 Implementation
Async MQTT 3.1.1 & 5.0 Client for Arduino ESP32 & ESP8266
MapsMessaging server supports the standard IoT protocols out of the box and enables server to server comms, plus filtering across all protocols
Enable MQTT 5 features for MQTT 3 Clients.
CommsChampion Ecosystem MQTT5 Client library and applications
MQTT Example collection for using HiveMQ MQTT client library
mqtt.go is a client library for the MQTTv5 protocol, written in Go. The users of the client library can use pull or push mechanism to receive messages.
Python uPClient for MQTT5 to be used by up-simulator and others
MQTT v3/v5 server written in golang using mochi-co/mqtt