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

Zelos - A very simple app for mobile teams - tasks and chats on desktop and mobile.

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

Google Groups - Google Groups allows you to create and participate in online forums and email-based groups with a rich experience for community conversations.

MailClark - The Slack bot for external communications

GroupServer - Email lists, with an integrated web interface, and control.