Toggl - Toggl is an online time tracking tool. It features 1-click time tracking and helps you see where your time goes. Free and paid versions are available.
Mailspring - Mailspring is a mail client for Mac, Windows and Linux.
Harvest - Simple time tracking, fast online invoicing, and powerful reporting software. Simplify employee timesheets and billing. Get started for free.
Geary - Geary is an email application built for GNOME 3.
RescueTime - Time management software that shows you how you spend your time & provides tools to help you be more productive.
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.