Teem - Cloud-based meeting room booking system
Mailspring - Mailspring is a mail client for Mac, Windows and Linux.
BOOKMEETINGROOM.COM - Book Meeting Room - Conference & Meeting Rooms Management
Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!
Meetio Room - Meeting Room Booking System
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.