heml
HEML is an open source markup language for building responsive email
... elements and style rules. Share them with the world, or keep em to yourself. Your choice. Email is hard. With dozens of popular email clients, each of which has its own quirks, it can be overwhelming to build an email that looks good and works well. Add in the challenge of getting your email to the inbox quickly, and it's enough to make anyone give up. HEML is a XML-based markup language designed for building emails. The goal is to make building emails feel as natural as building websites.