Amaya - W3C's
Editor/Browser
"Amaya started as an HTML + CSS style sheets editor. Since
that time it was extended to support XML and an increasing number
of XML applications such as the XHTML family, MathML, and SVG. It
allows all those vocabularies to be edited simultaneously in
compound documents."
"Amaya includes a collaborative annotation application based
on Resource Description Framework
(RDF),
XLink, and XPointer. Visit theAnnotea
projecthome page."