Mailspring - Mailspring is a mail client for Mac, Windows and Linux.

Google Contacts - Google Contacts is Google's contact management tool that is available in its free email service Gmail, as a standalone service, and as a part of Google's business-oriented suite of web apps Google Apps.

Thunderbird - Thunderbird is a free email application that's easy to set up and customize - and it's loaded with great features!

Apple Contacts App - Access and edit your contacts from personal, business, and other accounts with the Contacts app.

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.

Windows Contacts - Windows has many extraordinary organizers, and in the event that you include distributed storage, then you presumably have more.