Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!
Teem - Cloud-based meeting room booking system
Geary - Geary is an email application built for GNOME 3.
AskCody - Meeting management system for Outlook & Office 365.
Evolution - Apps/Evolution - GNOME Wiki!
TractionGuest - Safe, secure workplace for all.