DocBook is an XML vocabulary which enables you to create document content in a presentation-neutral form that captures the logical structure of the content. Using the DocBook Project XSL stylesheets, you can publish DocBook content as HTML pages and PDF files and other formats, including man pages, HTML Help, and JavaHelp.
The XNGR XML Browser is an XML browser framework, written in Java, that provides the functionality to associate Markers with directories, files, XML documents, and nodes in an XML document. Services and Actions can be associated to inspect and manage these marked items. Default services include a simple XML Editor and XML Viewer.
php xmllib is a class that is capable of parsing XML documents using only PHP code, without the need for a special extension library like Expat or any other XML parsing library. The code is very compact and efficient compared to competing libraries. However, it's not as feature-rich.