XMPP

Instant messaging platform. Backend in Go. Clients: Swift iOS, Java Android, JS webapp, scriptable command line; chatbots

Robust, Ubiquitous and Massively Scalable Messaging Platform (XMPP, MQTT, SIP Server)

An XMPP server licensed under the Open Source Apache License.

Event-driven networking engine written in Python.

ChatSecure is a free and open source encrypted chat client for iOS that supports OTR and OMEMO encryption over XMPP.

Jitsi is an audio/video and chat communicator that supports protocols such as SIP, XMPP/Jabber, IRC and many other useful features.

A modular and portable open source XMPP client library written in Java for Android and Java (SE) VMs

Web-based XMPP/Jabber chat written in JavaScript

Open-source XMPP client for Android

bridge between mattermost, IRC, gitter, xmpp, slack, discord, telegram, rocketchat, twitch, ssh-chat, zulip, whatsapp, keybase, matrix, microsoft teams, nextcloud, mumble, vk and more with REST API (mattermost not required!)

Chat SDK Android - Open Source Mobile Messenger

Cross-platform real-time collaboration client optimized for business and organizations.

MongooseIM is Erlang Solutions' robust, scalable and efficient XMPP server, aimed at large installations. Specifically designed for enterprise purposes, it is fault-tolerant and can utilise the resources of multiple clustered machines.

Tsung is a high-performance benchmark framework for various protocols including HTTP, XMPP, LDAP, etc.

XMPP for JavaScript

Strophe.js is an XMPP library for JavaScript

JavaScript-based multi-user chat client for XMPP.

QuickBlox iOS SDK for messaging and video calling

Movim - Decentralized social platform

Modern XMPP ("Jabber") Chat Client using GTK/Vala