Xopus is a generic in-browser XML editor that takes any combination of XML, Schema (XSD) and XSL and makes it directly editable. It works in any XML/XSL-enabled browser. Currently only Microsoft Internet Explorer 5.5 on the Microsoft Windows platform.
Go there and try at http://q42.nl/editors.html while reading on http://www.q42.nl/xopus.
PS: Xopus is part of Wyona!
PPS: Wyona is used at NZZ!
