Whimsical Wireframes - Lightning fast wireframing with real-time collaboration.
HTMLEmail.io - Responsive HTML email templates for startups & developers
Figma Map Maker - Figma plugin to generate map, supporting Google Maps, Mapbox
Templates by Email Monster - Hundreds of free, responsive email templates. Pick and edit.
Invision - Prototyping and collaboration for design teams
MJML - The open source framework for responsive emails