HydroMark is a WYSIWYG Markdown editor add-in for Microsoft OneNote. Type Markdown naturally inside OneNote and see formatted output instantly It turns OneNote into a real technical-note workspace: code highlighting, LaTeX math, Mermaid / ZenUML diagrams, slash commands, tables, and source/rendered dual views. Plus page-width control and seamless import/export for when you do need a file. Built for developers, students, and technical writers who love OneNote but can’t live without Markdown.