Hiver - Manage Customer Support, Sales and Projects right from your Gmail inbox. Collaborate with Shared Labels, Shared Contacts, email notes, email reminders and email templates

ContactRescue - Magically get your address book up-to-date and accurate

Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.

Cardhop - The Mac contacts app you'll want to use.

MailClark - The Slack bot for external communications

Microsoft Outlook - Organize your world. Outlook’s email and calendar tools help you communicate, stay on top of what matters, and get things done.