Mosaico.io - Outstanding opensource email template editor by VOXmail.it
MailDrop - maildrop is a Mail delivery agent used by the Courier Mail Server. The maildrop MDA also includes filtering functionality. maildrop receives mail via stdin and delivers in both Maildir and mbox formats.
Topol.io - Create professional Email templates easily - Drag & Drop Email Builder.
InboxKitten - An open-source, disposable email service 💌
BeeFree.io - Bee is MailUp's drag-&-drop editor for responsive design emails.
Unroll.me - Unroll.