Jaxe is a open source, multiplatform Java XML editor that specially designed for advanced user or web developer to create a simple end-user interface for a given document-oriented XML language Examples include XHTML strict and simplified Docbook.
It’s not "WYSIWYG" (What You See Is What You Get), it is "WYSIWYM" (What You See Is What You Mean) editor. As with all good XML editor, display is an operation independent from data input. Features include: graphical document-oriented user interface (not just tree-like), customizable user interface for a given document type, validation at edition time, HTML preview with an XSL style sheet, Easy to exports XML and PDF with XSLT and XSL-FO style sheets, complete document validation etc..
Download : Jaxe XML editor