Markdown

Markdown is a text-to-HTML conversion tool for web writers, allowing you to write using an easy-to-read, easy-to-write plain text format, then convert it to structurally valid XHTML (or HTML).

Althought I prefer Textile for its table support and other niceties, Markdown makes for slightly more readable text when writing essays.

Implementations:

Date Link Notes
Oct’11 MMD A C language implementation of MultiMarkdown.
Mou A web developer-oriented app.
Multimarkdown Composer Another Mac app.
Jan 5 readown A Cocoa viewer that wraps the PHP renderer.
Dec 25 discount A C implementation.
Oct 16 Pandoc A markup converter written in Haskell with support for it
Older WMD an amazing JavaScript editor specifically tailored for using Markdown.
Make.text a bookmarklet for translating a web page into Markdown
PyMarkdown for Python, obviously.
python-markdown2 a second Python implementation, with some improvements.
BlueCloth for Ruby
PHP implementation
C# / .NET implementation
Partial implementation in JavaScript
Showdown a better one
A more complete list maintained by Franรงois Granger, who is developing a markup converter.