Marked is a previewer (not an editor) for MultiMarkdown, Markdown, Text and HTML files. It watches the original file for changes, updating the preview any time the file is saved. With a full set of customization options and preview styles, Marked adds an ideal “live” Markdown preview to any text editor.
You can also use a custom processor with Marked, making it compatible with any form of Markdown or even other languages such as Textile.

Requirements: Mac OS X 10.6 or later