Corel just announced the availability of a new beta version of WordPerfect that provides support for both Open XML as well as ODF. They provide for a number of choices in document formats, with Open XML and ODF being the two latest supported formats. http://home.businesswire.com/portal/site/google/index.jsp?ndmViewId=news_view&newsId=20071003005854&newsLang=en
Here is a quote from Nick Davies (VP and GM of graphics and productivity at Corel):
"Open standards are increasingly important for our customers, especially in government. A multi-format approach allows Corel to provide our customers with maximum compatibility and archival options, and harnesses our deep expertise in file formats to deliver flexible document solutions for our customers."
I haven't had a chance to play around with the beta, but I hope to soon. Another thing I noticed in the press release is that they have an integrated XML editor that allows you to work with custom XML as well. It would be cool to see how this integrates with Open XML's custom XML support.