Messaging GitHub Repositories (2026) · Open Source Tools

Java client for NATS

High-Performance server for NATS.io, the cloud and edge native messaging system.

A community-driven replacement for JSQMessagesViewController

signal-cli provides an unofficial commandline, JSON-RPC and dbus interface for the Signal messenger.

The most widely used PHP client for RabbitMQ

A Messaging Layer Security (RFC 9420, MLS) implementation in TypeScript

A dead simple Go library for sending notifications to various messaging services.

A modern high-performance open source message queuing system

Messaging library for Python.

Apache ActiveMQ

Telegram Server written in C# (Unofficial) - messaging, channels, media, secret chats and voice/video calls.

Telegram MCP server powered by Telethon to let MCP clients read chats, manage groups, and send/modify messages, media, contacts, and settings.

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

MQTT Server/MQTT Broker - Scalable Distributed MQTT Message Broker for IoT in the 5G Era

Lightweight message bus interface for .NET (pub/sub and request-response) with transport plugins for popular message brokers.

Eclipse Hono™ Project

Async .NET client for NATS: pub/sub, request/reply, JetStream, KV, Object Store, Services

Threema App for iOS.

A multi-protocol gateway for the Web using ActivityStream messages.

Highly optimized, extremely modular and very flexible XMPP/Jabber server