Mark Twain is a Node.js library that parses Markdown files into a structured JavaScript object using JsonML, making it easier to process and manipulate Markdown content programmatically. It's designed for developers who need to work with Markdown data in a more structured format, particularly those building tools that convert Markdown to other formats like React components. The library handles both the Markdown content and any YAML frontmatter, providing a clean separation between metadata and content structure.