The English Editor II is an XML editor for BeOS. It also handles email and Usenet messages. It is currently incomplete, but more or less usable. Give it a try if you're interested in seeing an editor that doesn't look much like other text editors.
The "Tab" key is the "tag" key--use it to insert new XML tags (such as "bold", "italic", etc.) or change the tag-names of existing ones.
Sources obtained from http://www.folta.net/steve/EnglishEditorII/
"Sources are made available under an MIT-style license."