de-xhtml is an XHTML-to-HTML XSLT tool by Joseph Walton. Three things to consider:
- Documents stored as XHTML are easier to process than HTML.
- Documents stored as XHTML are more future-proof than HTML.
- Documents stored as XHTML are a pain in the ass to serve properly (due to lack of browser support, natch), but serving these documents as
text/html is largely useless.
Joseph's tool helps you realize the benefits of points one and two without the hassle of point three.
More info on Joseph's site.