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
MailStore - MailStore Home - A 100% free single-private-user desktop solution
Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.
MailSteward - MailSteward : The Ultimate E-mail Manager for Mac OS X
MailClark - The Slack bot for external communications
Gmvault - Backup the emails in your Gmail account.