Webiny - The Enterprise CMS platform that you can host on your cloud
HTMLEmail.io - Responsive HTML email templates for startups & developers
Bubble.io - Building tech is slow and expensive. Bubble is the most powerful no-code platform for creating digital products.
Templates by Email Monster - Hundreds of free, responsive email templates. Pick and edit.
Kodular - Much more than a modern app creator without coding
MJML - The open source framework for responsive emails