html2texy! is a converter from (X)HTML to the Texy! mark up language. It's implemented as an XSLT template and intended for use from PHP (uses a couple of calls to PHP-specific extensions to XSLT).
Texy! is a (yet another) mark up language resembling Markdown, Textila, or reStructuredText.
You can try out html2texy! here: http://webkitchen.cz/lab/html2texy/demo
Note that this project isn't supported anymore and you are welcome to fork it.