Listmonk - Send e-mail campaigns from a powerful dashboard. High performance and features packed into one app.
Templates by Email Monster - Hundreds of free, responsive email templates. Pick and edit.
Sendy - Sendy is a self hosted newsletter app that sends emails 100x cheaper via Amazon SES
MJML - The open source framework for responsive emails
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
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.