Signal is a messaging app for simple private communication with friends. Signal uses your phone's data connection (WiFi/3G/4G) to communicate securely, optionally supports plain SMS/MMS to function as a unified messenger, and can also encrypt the stored messages on your phone.

Signal-Android - A private messenger for Android, alternative to WhatsApp

Caprine is an unofficial and privacy focused Facebook Messenger app with many useful features. It has support for Work Chat: Messenger for Workplace, You can send code blocks by using Markdown syntax. It is built with Electron framework.

Caprine - Elegant Facebook Messenger Desktop App

ejabberd is a distributed, fault-tolerant technology that allows the creation of large-scale instant messaging applications. The server can reliably support thousands of simultaneous users on a single node and has been designed to provide exceptional standards of fault tolerance. As an open source technology, based on industry-standards, ejabberd can be used to build bespoke solutions very cost effectively.

ejabberd - Robust, Scalable and Extensible XMPP Server

Slackin is a little server that enables public access to Slack server. It is like Freenode but on Slack.

Slackin - Public Slack organizations made easy

 With the rise of government surveillance programs, Tox, a FOSS initiative, aims to be an easy to use, all-in-one communication platform that ensures full privacy and secure message delivery. Tox must use UDP simply because hole punching with TCP is not as reliable. However, Tox does use TCP relays as a fallback if it encounters a firewall that prevents UDP hole punching.
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It helps to chat instantly across the globe with Tox's secure messages. It supports Encrypted voice calls, Screen sharing, File sharing, Video calls, Share with group or team. Tox has no central servers that can be raided, shut down, or forced to turn over data — the network is made up of its users. 

With the rise of government surveillance programs, Tox, a FOSS initiative, aims to be an easy to use, all-in-one communication platform that ensures full privacy and secure message delivery. Tox must use UDP simply because hole punching with TCP is not as reliable. However, Tox does use TCP relays as a fallback if it encounters a firewall that prevents UDP hole punching.

Tox - The future of online communications.

Signal sends high-quality group, text, voice, video, document, and picture messages anywhere in the world. Signal messages and calls are always end-to-end encrypted and painstakingly engineered to keep your communication safe. 

Signal - Secure Messaging

Rocket.Chat is a Web Chat Server, developed in JavaScript, using the Meteor fullstack framework.
It is a great solution for communities and companies wanting to privately host their own chat service or for developers looking forward to build and evolve their own chat platforms. Its features include File sharing, Video conferencing, Screen sharing, Live chat, Link preview and lot more. 

RocketChat - The ultimate open source web chat platform

Gitter is designed to make community messaging, collaboration and discovery as smooth and simple as possible. You can easily create, organise and grow your communities, inviting others to join just in one click. Gitter is an instant messaging and chat room system for developers and users of GitHub repositories. Gitter is similar to IRC and Slack. Unlike IRC, and like Slack, it automatically logs all messages in the cloud.

Gitter - Community for Software Developers

 Ricochet is an experimental kind of instant messaging that doesn't trust anyone with your identity, your contact list, or your communications. Ricochet is a peer-to-peer instant messaging system built on the Tor Network hidden services. Your login is your hidden service address, and contacts connect to you (not an intermediate server) through Tor. The rendezvous system makes it extremely hard for anyone to learn your identity from your address.

Ricochet - Anonymous peer-to-peer instant messaging

Hubot is a chat bot, modeled after GitHub's Campfire bot. It is extendable with community scripts and your own custom scripts, and can work on many different chat services.

Hubot - A Chat Bot for your Company

Hubl.in is a free and open source video conference solution built with love and designed with ethics in mind. It's the best way to initiate a communication anywhere with anybody and brings real time conversation to the next level. Hubl.in allows free communication without additional plugins.

Hublin - An easy and free video conference service

Zulip is a powerful, open source group chat application. It supports both private messaging and group chats via conversation streams. Zulip also supports fast search, drag-and-drop file uploads, image previews, group private messages, audible notifications, missed-message emails, desktop apps, and much more.

Zulip - Group Chat

 Telegram is a messaging app with a focus on speed and security. It’s superfast, simple and free. This repo contains the official source code for Telegram App for Android. We welcome all developers to use our API and source code to create applications on our platform. There are several things we require from all developers for the moment.

Telegram - Telegram for Android

Element is a messaging app that lets you chat securely with your family and friends. The communication is default end-to-end encrypted, cross-signed device verification and decentralisation to choose who you trust with your data. Element is unique. You own your data and decide where it lives. Element lets you talk securely to anyone, regardless of their app. It supports unlimited voice, video and messaging. It is built on Matrix.

Element - Secure and independent communication, connected via Matrix

NebulaChat is an open source mtproto server written in golang with compatible telegram client. mproto protocol is designed for access to a server API from applications running on mobile devices. 

NebulaChat - Open source mtproto server written in golang with compatible telegram client

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