vBulletin - Build a community website with the leading forum software, vBulletin 5 Connect, or in the cloud on vB Cloud!
Mailspring - Mailspring is a mail client for Mac, Windows and Linux.
XenForo - Intuitive. Social. Engaging. Fast. XenForo brings a fresh outlook to forum software.
Geary - Geary is an email application built for GNOME 3.
Flarum - Flarum is the next-generation forum software that makes online discussion fun. It's simple, fast, and free.
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.