Link: http://xml-copy-editor.sourceforge.net/
Source Author or Organization: Gerald Schmidt

XML Copy Editor is a fast, free, validating XML editor. Binaries are released for Windows and Linux simultaneously. Free, open-source, multi-platform, under active development. Validation against Relax NG schemas and XSD are built in (DTD's too, of course), with DocBook, Topic Maps, DITA, Open Laszlo, TEI, XHTML and other vocabularies already added. XSLT built-in too. Has mode for large documents. Folds and unfolds tags. Can lock tags so editing is restricted to content areas. XML Copy Editor is available in Chinese (simplified and traditional), English, French, German, Slovak, Swedish and Ukrainian. There are Linux packages for Arch, Fedora Core 4 and 5/6, Slackware and Ubuntu.