Script/website: michelf.com/projects/php-markdown/
Requirements: PHP
Installation time: Varies. Wordpress plugin installation takes less than a minute
Difficulty: Easy
License: Free, BSD-style open source
Download: PHP source in zip
API: N/A
Author Description: “The Markdown syntax allows you to write text naturally and format it without using HTML tags. More importantly: in Markdown format, your text stays enjoyable to read for a human being, and this is true enough that it makes a Markdown document publishable as-is, as plain text. If you are using text-formatted email, you already know some part of the syntax.”

screenshot of using PHP Markdown through Dingus demo preview

Based on John Gruber’s Markdown (Perl), PHP Markdown can be used a Wordpress plugin by copying over the markdown.php file from the zip file to the wp-content/plugins directory. There is an official demo called Dingus here. The screenshot above shows my example of using PHP Markdown syntax through Dingus.

The function Markdown($text) inside markdown.php is passed a text string and returns the marked down version, so incorporating this into another program where you want to markdownify the text is pretty straightforward, although the file is a bit on the bulky side at 55k. Would be more convenient if a version without Wordpress and bBlog code inside it were provided in the zip package. The most recent version as of this writing was September 5, 2005.