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
Templates by Email Monster - Hundreds of free, responsive email templates. Pick and edit.
Clean Email - Clean Email is an online service that empowers you to take control of your mailbox.
MJML - The open source framework for responsive emails
MailClark - The Slack bot for external communications
Stripo - Stripo is an all-in-one email design platform. We enable our clients to build emails of any complexity, including interactive AMP emails, really fast and easy.