Mosaico.io - Outstanding opensource email template editor by VOXmail.it
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.
Topol.io - Create professional Email templates easily - Drag & Drop Email Builder.
MJML - The open source framework for responsive emails
BeeFree.io - Bee is MailUp's drag-&-drop editor for responsive design emails.
MailChimp - MailChimp is the best way to design, send, and share email newsletters.