HTACG, the HTML Tidy Advocacy Community Group, is an organization dedicated to the maintenance and advancement of HTML Tidy, a tool originally created by the World Wide Web Consortium (W3C) to help clean up and fix HTML code. Their mission is to ensure that web content is easily readable and adheres to modern web standards. The group focuses on improving the HTML Tidy codebase, adding new features, and facilitating discussions around best practices for web development.