Material UI: Comprehensive React component library that implements Google's Material Design. Free forever.

MJML: the only framework that makes responsive email easy

Font Awesome split to individual SVG and PNG files of different sizes along with Node.JS based generator

Working to improve the user experience, accessibility, performance, consistency, and reliability of email markup

Pre-grid responsive layout toolkit for Sass, now deprecated

Automatically switch to a darker or a lighter version of an element depending on the brightness of images behind it.

Beautiful responsive email templates with code as beautiful as email templates can be

A professional front-end template for building fast, robust, and adaptable web apps or sites.