Hi, I'm currently writing my own wiki, partly to learn about distributed version control systems. As part of that, I'm implementing a creole parser.
Its implemented in PHP5.1+, and uses the DOM extension to build the XHTML/HTML of the document.
My current implementation, testsuite, and testsuite output is available at http://homepage.ntlworld.com/jared.williams/creole/Creole.zip.
It should be, if not close to an 0.4 implementation. It guarantees valid XML output (unless bug in libxml) and should always output valid XHTML. Has a few specific engine quirks, like using <object> for local inclusions, instead of <img>, and as such output isn't intended for displaying directly to a browser.