Mjml

Mjml is a lightweight app that makes responsive e-mail smooth. You import and manage templates, edit your email with live rendering, customize your environment and send e-mails. The presets section will provide a selection of the best community templates using this app. If you want your template to appear in this section, you can submit a pull request on Github.
Mjml's Github link :
https://github.com/mjmlio/mjml