Targeted.io - Test your email designs across 30+ clients before you send'm
MJML - The open source framework for responsive emails
Really Good Emails - A large collection of good product email design.
Getform - Smart form endpoints. The modern way to build the form backend.
Stamplia - High converting and beautifully designed email templates
Mail Designer 365 - Discover Mail Designer 365, the easiest way to design mobile-optimized HTML emails, templates and newsletter designs. Your HTML email designer for Mac.