Mighty Networks - Mighty Networks enables entrepreneurs, organizations, and companies to create and grow a community-powered brand.
Mailspring - Mailspring is a mail client for Mac, Windows and Linux.
Bigtent - BigTent is a web-based organization and communication portal for groups.
Geary - Geary is an email application built for GNOME 3.
Nabble - Nabble is a forum software that are embeddable and fully customizable with scripting language.
The Bat - The Bat! is a secure desktop email client for Windows, designed to protect your correspondence against third-parties and to save your time.