Tagfree2000 Contains XML, DTD, and SMIL editors. [Commercial]
Stylus Studio Sonic Software's platform for an XML development environment that includes an XML Schema editor, XSLT editor, XML-XML mapper, debugging and document wizards. [Commercial]
Wikipedia Links
XML Editor In the field of computer markup languages, XML files can be edited in plain text in an editor program such as Vim, with all the code visible. There are also WYSIWYG XML editors that hide the code in the background and present the content to the user in a more user-friendly format, approximating the rendered version. This is helpful for situations where people who are not fluent in XML code need to enter information in XML based documents such as time sheets and expenditure reports. And even if the user is familiar with XML, it is often faster and more convenient to use an XML editor and let it take care of syntax details.