Windows/Mac/Linux/Web: Pandoc is a powerful command-line tool for converting text documents between formats like Markdown to HTML, HTML to MediaWiki, and more.
Pandoc reads markdown languages such as HTML, LaTeX, and reStructuredText and converts them to other markdown languages and document formats such as HTML, LaTeX, XML, RTF, PDF, ePUB and more.
The screenshot above is of the web-based Pandoc tool, handy for demonstrating basic application of Pandoc but fairly limited in comparison to the command-line tool available for Windows, Mac and Linux operating systems.
Pandoc is a free, cross-platform, application. Visit the link below to read more about it, including a detailed user's guide and examples on converting between formats.