Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.
Zero Email App - Think of it as a private Google PageRank for your inbox
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
Tomba.io - Tomba is the leading solution to find and verify professional email addresses. Start using Tomba and connect with the people that matter for your business.
MailClark - The Slack bot for external communications
Hunter - Find all the email addresses related to a domain