Tools

A fully featured open source mail delivery platform for incoming & outgoing e-mail

Web-based XMPP/Jabber chat written in JavaScript

Mail-in-a-Box helps individuals take back control of their email by defining a one-click, easy-to-deploy SMTP+everything else server: a mail server in a box.

Friendica Communications Platform

Mbin: a federated content aggregator, voting, discussion and microblogging platform

Cypht: Lightweight Open Source webmail aggregator [PHP, JS]. Supports IMAP/SMTP, JMAP and EWS (Exchange Web Services)

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

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

Baïkal is a Calendar+Contacts server

The osTicket open source ticketing system official project repository, for versions 1.8 and later

Secure SMTP server implementation from the OpenBSD project.

A modern IRC server (daemon/ircd) written in Go.

An open-source platform for legally compliant email archiving.

Secure direct video group chat