Federated microblogging server.

Advanced forum / community solution based on Ruby and JS.

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).

Push notifications to phone or desktop using HTTP PUT/POST, with Android app, CLI and web app, similar to Pushover and Gotify.

Customer communication platform (alternative to Intercom and Zendesk).

WebRTC application that uses Jitsi Videobridge to provide high quality, scalable video conferences.

Zulip is a powerful, open source group chat application.

High performance, self-hosted newsletter and mailing list manager with a modern dashboard.

Production-ready fullstack but simple mail server (SMTP, IMAP, LDAP, Antispam, Antivirus, etc.) running inside a container. Only configuration files, no SQL database.

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.

Complete and fully featured mail server for use by websites & web servers.

Delightfully simple forums. Flarum is the next-generation forum software that makes online discussion fun again.

Knowledge-based community software. You can use it to quickly build your Q&A community for product technical support, customer support, user communication, and more.

Turns any Ubuntu server into a fully functional mail server with one command.

Forum software built for the modern web.

Notification server with Android and CLI clients (alternative to PushBullet).

Link aggregator for the fediverse (alternative to Reddit).

Distributed social networking server.

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

Fully-featured Matrix client for Web, iOS & Android.

All-in-one mail server with JMAP, IMAP4, and SMTP support and a wide range of modern features.

Mail server suite based on Dovecot, Postfix and other open source software, that provides a modern Web UI for administration.

The most private and secure chat and applications platform - now with double ratchet E2E encryption.

Decentralized app-like microblogging server/SNS for the Fediverse, using the ActivityPub protocol like GNU social and Mastodon.

Screego is a simple tool to quickly share your screen to one or multiple people via web browser.

Language-agnostic real-time messaging (Websocket or SockJS) server.

Conversational app builder (alternative to Typeform and Landbot).

Marketing automation software (email, social and more).

Supports real-time sharing of audio, video, slides (with whiteboard controls), chat, and the screen. Instructors can engage remote students with polling, emojis, and breakout rooms.

General-purpose, lightweight, minimalist WebRTC Server.

Low-latency, high quality voice/text chat software.

Simple yet full-featured mail server as a set of Docker images.

Browser-based IMAP client with an application-like user interface.

Ethical photo sharing platform, powered by ActivityPub federation (alternative to Instagram).

Open source email alias solution to protect your email address. Comes with browser extensions and mobile apps.

Flexible kit for private social networks.

XMPP instant messaging server.

Self-hosted web IRC client.

All-in-one mail server that implements SMTP (both MTA and MX) and IMAP. Replaces Postfix, Dovecot, OpenDKIM, OpenSPF, OpenDMARC with single daemon.

Complete e-mail solution with IMAP4, SMTP, SPF, DKIM, DMARC, MTA-STS, DANE and DNSSEC, reputation-based and content-based junk filtering, Internationalization (IDNA), automatic TLS with ACME and Let's Encrypt, account autoconfiguration, and webmail.

Fast, highly extensible, and event driven SMTP server.

Lightweight and simple comment engine, which doesn't spy on users. It can be embedded into blogs, articles or any other place where readers add comments.

Virtual office / virtual conference application presented as a 16-bit RPG video game.

Lightweight commenting server written in Python and Javascript. It aims to be a drop-in replacement for Disqus.

Scalable open source cross-platform telephony platform.

Email forwarding service for creating aliases.

Simple, secure, fast real-time video conferences up to 4k and 60fps, compatible with all browsers and platforms.

Server for [Matrix](https://matrix.org/), an open standard for decentralized persistent communication.