This is a clone/fork of Netlify's MailMe repository. That one is no longer maintained, but this one is as it's an important dependency to GoTrue the software behind Supabase Auth.
MailMe is meant to deliver transaction mails with a template that can be loaded from a URL. If no template is present from the URL it will fall back to a default template.
This makes it easy to deploy your mail templates to a CDN (with Netlify) and have an easy workflow to work with the mails and preview them directly in the browser.