Awesome Mails - Awesome Mails creates beautiful image map emails, featuring an easy to use drag-and-drop editor...
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.
Marble Responsive Email Designer - Marble helps you design beautiful and mobile-friendly emails and newsletters.
MJML - The open source framework for responsive emails
Kingmailer - Kingmailer helps you send, receive and route/forward emails.
BeeFree.io - Bee is MailUp's drag-&-drop editor for responsive design emails.