Amaya
“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.”