Vectr - Free vector graphics editor. A simple yet powerful web and desktop cross-platform tool for everyone.
HTMLEmail.io - Responsive HTML email templates for startups & developers
Vecteezy Editor - Free Online Vector Editor - Design and customize SVG illustrations and graphics quickly and easily in your browser.
Templates by Email Monster - Hundreds of free, responsive email templates. Pick and edit.
Inkscape - Inkscape is a free, open source professional vector graphics editor for Windows, Mac OS X and Linux.
MJML - The open source framework for responsive emails