Pandoc is a universal document converter

Pandoc is a Swiss army knife for text, a document converter with a dizzying set of formats from the elegant and utilitarian Markdown to the enervating and universal Microsoft Word Doc. Roff, LaTex, even PDF, it's mostly in there! (via Hacker News)

Pandoc understands a number of useful markdown syntax extensions, including document metadata (title, author, date); footnotes; tables; definition lists; superscript and subscript; strikeout; enhanced ordered lists (start number and numbering style are significant); running example lists; delimited code blocks with syntax highlighting; smart quotes, dashes, and ellipses; markdown inside HTML blocks; and inline LaTeX. If strict markdown compatibility is desired, all of these extensions can be turned off.

There's an online version, with downloads for offline use. Looks like you can integrate them easily into workflows, too. It doesn't convert WordStar, sadly, but you can't have everything.

Previously: This "Weird Units Calculator" can convert watts into T-Rex bites and lightsabers