Rocket.Chat
46kCommunications platform that puts data protection first (alternative to Gitter.im and Slack).
SelfHostHub lists 46 open-source Custom Communication Systems projects you can host on your own server. The most-starred on GitHub are Rocket.Chat (46,288 stars), Novu (40,168 stars) and Mattermost (39,373 stars). 23 of them document a Docker install, and 12 offer a live demo you can try first.
Replacing a paid app? See open-source alternatives to Slack, open-source alternatives to Discord.
Communications platform that puts data protection first (alternative to Gitter.im and Slack).
Notification infrastructure for developers.
Platform for secure collaboration across the entire software development lifecycle, can be integrated with Gitlab (alternative to Slack).
Customer communication platform (alternative to Intercom and Zendesk).
Push notifications to phone or desktop using HTTP PUT/POST, with Android app, CLI and web app, similar to Pushover and Gotify.
Zulip is a powerful, open source group chat application.
The most private and secure chat and applications platform - now with double ratchet E2E encryption.
Apprise allows you to send a notification to almost all of the most popular notification services available to us today such as: Telegram, Discord, Slack, Amazon SNS, Gotify, etc.
Notification server with Android and CLI clients (alternative to PushBullet).
WhatsApp API gateway exposing messaging as REST endpoints, with a web dashboard, multi-account sessions, and webhook events (alternative to WhatsApp Business API providers).
Fully-featured Matrix client for Web, iOS & Android.
Instant messaging platform. Backend in Go. Clients: Swift iOS, Java Android, JS webapp, scriptable command line; chatbots.
Language-agnostic real-time messaging (Websocket or SockJS) server.
Screego is a simple tool to quickly share your screen to one or multiple people via web browser.
Instant messaging and VoIP platform built for friends, groups, and communities (alternative to Discord).
Conversational app builder (alternative to Typeform and Landbot).
Low-latency, high quality voice/text chat software.
Virtual office / virtual conference application presented as a 16-bit RPG video game.
Server for [Matrix](https://matrix.org/), an open standard for decentralized persistent communication.
Share sensitive information securely with self-destructing links that are only viewable once.
Distributed, secure messenger with audio and video chat capabilities.
Stoat is a user-first chat platform built with modern web technologies.
Web Whiteboard to collaborate in real-time on schemas, drawings, and notes.
High-performance and feature-rich chat server for Matrix, and the successor to conduwuit (fork of Conduit).
Realtime server for reliable two-way communication over WebSockets, Server-sent events, etc.
Peer-to-peer chat app that is serverless, decentralized, and ephemeral.
Live Support chat for your website.
Secured and decentralized communication system. Offers decentralized chat, forums, messaging, file transfer.
Whistleblowing software enabling anyone to easily set up and maintain a secure reporting platform.
Federated, end-to-end encrypted messaging service for the web, iOS, and Android, supporting text, photos, video, and WebRTC video and audio calls.
Anonymously share files, browse and publish _freesites_ (web sites accessible only through Hyphanet) and chat on forums.
A simple, fast, and reliable chat server powered by Matrix.
Multichannel notification server with support for Email, Mobile Push, Web Push, SMS, messaging and a javascript plugin.
One-Time-Secret sharing platform with a symmetric 256bit AES encryption in the browser.
Spectrum 2 is an open source instant messaging transport. It allows users to chat together even when they are using different IM networks.
Keep secrets out of emails or chat logs, share them using secure links with passphrase and expiration dates.
Notification server for relaying push notifications via Matrix, similar to PushBullet and Gotify.
All-in-one customer engagement platform from lead-gen to post-sales, from WhatsApp to your website. With omni-channel live agents and AI-powered chatbots (alternative to Intercom, Zendesk, Tawk.to and Tidio).
Next-Gen self-hosted chat server and clients.
Community-driven Matrix homeserver, the continuation of conduwuit focusing on user experience and new features (fork of Conduit).
Software framework for decentralized, peer-to-peer networking.
Online whiteboard, audio/video conferencing, screen sharing, shared code editing and optional session recording/playback.
Universal communication platform which preserves the user's privacy and freedoms.
Web-based, end-to-end encrypted email platform that uses an independent PKI.
Platform for your corporate communications, based on the advanced architecture, with support for UltraHD video conferencing, built-in messenger with personal and group chats, and a free version for up to 1,000 users.
Instant messaging and collaboration tool with private and group chat rooms, continuous voice and video meetings, files sharing, issue tracking with integrated task board (alternative to Slack).
By GitHub stars, the top projects in this category are Rocket.Chat (46,288 stars), Novu (40,168 stars) and Mattermost (39,373 stars).
46 projects are currently listed in the Custom Communication Systems category on SelfHostHub.
The most common licences in this category are MIT (12), Apache-2.0 (10) and AGPL-3.0 (7).
23 of the 46 projects list Docker as a supported platform. Check each project's documentation for the exact install steps.