I’ve collected few of the best free and open source email templates to help you improve email experience for your projects.

• MJML - MJML is responsive by design on most-popular email clients, even Outlook. Write less code, save time and code more efficiently with MJML’s semantic syntax.
• Email Blueprints — Email Blueprints is a collection of HTML email templates that can serve as a solid foundation and starting point for the design of emails. They include template language elements that make them customizable when imported into a MailChimp account, as well as merge tags that will generate dynamic content when sent through MailChimp.*
• Ink — Ink is a responsive email framework, used to make HTML emails look great on any client or device. It includes a 12-column grid, as well as some simple UI elements for rapid prototyping.*
• Send With Us — The sendwithus Open Source Template Project is a collection of free email templates created and managed by the sendwithus team and community. Anyone may contribute new themes and templates, or make impactful updates to the existing ones.*
• Responsive HTML Email Template — This template is designed to work on all major email platforms and it is built with media query, making it responsive for smartphones that supports media query. It serves as a foundation that has been tested and thoroughly reviewed for compatibility, very easy to customize and make changes.*
• Email Boilerplate — Use these code examples as a guideline for formatting your HTML email to avoid some of the major styling pitfalls in HTML email design. You may want to create your own template based on these snippets or just pick and choose the ones that fix your specific rendering issue(s).*
• Salted — Creating HTML email that renders well across most clients is surprisingly hard, especially when you want it to be responsive. Salted is a responsive email template that tries to make things easier.*
• Transactional E-mail Templates — Transactional HTML emails often get neglected. Styling HTML email is painful. Tables, inline CSS, unsupported CSS, desktop clients, web clients, mobile clients, various devices, various providers.*
• Cerberus — Coding regular emails is hard enough by itself. Making them responsive shouldn’t add to the headache. A few simple, but solid patterns are all that’s needed to optimize emails for small screens.*
• Antwort — Antwort offers responsive layouts for Email that both fits and adapts to client widths. Don’t underwhelm desktop users with single column layouts that work for mobile. Antwort offers columns on desktop that automatically become rows on mobile.