Artboard Studio - Online graphic design app mainly focused on product mockups.
Templates by Email Monster - Hundreds of free, responsive email templates. Pick and edit.
Vectr - Free vector graphics editor. A simple yet powerful web and desktop cross-platform tool for everyone.
MJML - The open source framework for responsive emails
Canva - Canva is a graphic-design platform with a drag-and-drop interface to create print or visual content while providing templates, images, and fonts. Canva makes graphic design more straightforward and accessible regardless of skill level.
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.