Amaya
You must read the disclaimer before downloading.
W3C's Editor/Browser
Amaya is a Web editor, i.e. a tool used to create and update documents directly on the Web. Browsing features are seamlessly integrated with the editing and remote access features in a uniform environment. This follows the original vision of the Web as a space for collaboration and not just a one-way publishing medium.
Work on Amaya started at W3C in 1996 to showcase Web technologies in a fully-featured Web client. The main motivation for developing Amaya was to provide a framework that can integrate as many W3C technologies as possible. It is used to demonstrate these technologies in action while taking advantage of their combination in a single, consistent environment.
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 the Annotea project home page.
Amaya - Open Source
Amaya is an open source software project hosted by W3C. You are invited to contribute in many forms (documentation, translation, writing code, fixing bugs, porting to other platforms...).
The Amaya software is written in C and is available for Windows, Unix platforms and MacOS X.
Amaya Team
The application is jointly developed by W3C and the WAM (Web, Adaptation and Multimedia) project at INRIA. The core team includes: Irène Vatton (Project lead, INRIA), Laurent Carcone (W3C), Vincent Quint (INRIA).


a note on Amaya and screen reader accessibility
Was checking out your site and wanted to pass this bit of information to you. Amaya is cited here as an accessible html editor and browser. Unfortunately, this is incorrect. For users of screen reading assistive technology, the application's menus and dialogues are about 97% accessible. The area where text is entered and edited, however, is not for anyone using the following screen readers:
Jaws for windows 10.0 and 11.0
Window eyes 7.0
NVDA 2010
The window class used is something called wx Amaya canvas which none of these products have any idea what to do with. There are three accessible web page creation applications I have encountered so far. They are KompoZer, Arachnophelia 4.0 and adobe dreamweaver cs5. The first 2 are free. The third is not. Html Kit is about 75% accessible but the menus do not come across properly to screen readers because of how they were coded and how the controls and window classes were assigned to them. Amaya, however, is not accessible for actually writing or editing content. About all you can do with it is add themes and backgrounds to a page you have already written. Any blind person who downloads and installs it on a windows platform in it's current state (version 11.3) will be in for an unpleasant surprise. He will be able to label all his toolbar graphics since they all have nice tooltips on them, he will be able to navigate through the menus. But, when he goes to try and actually write his webpage, tempers will be lost, four-letter words will be said, desks will be pounded and execrations will be heaped upon the head of anyone who directed them to this "accessible" solution.
Many thanks and have a nice day, :)
Alex
Long-time jaws user