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