Libxml2 is the XML C library developed for the Gnome project. The library code is portable (to Linux, Unix, Windows, embedded systems, etc.) and modular; most of the extensions can be compiled out. Libxml2 implements a number of existing standards related to markup languages, including the XML standard, Namespaces in XML, XML Base, Relax NG, RFC 2396, XPath, XPointer, HTML4, XInclude, SGML Catalogs, and XML Catalogs. In most cases, libxml tries to implement the specifications in a relatively strict way. To some extent, it provides support for the following specifications, but doesn't claim to implement them: DOM, FTP client, HTTP client, and SAX2. Support for W3C XML Schemas is in progress. It includes xmllint, a command line XML validator.
Libxslt is a C library for GNOME which allows developers to work with XSLT. It is based on libxml for XML parsing, tree manipulation, and XPath support. Also included is 'xsltproc', a command line XSLT processor. The library is written in plain C, making as few assumptions as possible, and sticking closely to ANSI C/POSIX for easy embedding. It should work on Linux, Unix, and Windows. Though not designed primarily with performances in mind, libxslt seems to be a relatively fast processor. It also include full support for the EXSLT set of extension functions as well as some common extensions present in other XSLT engines.
xopus is a browser-based (Mozilla, IE) in-place WYSIWYG XML editor. It works similarly to a word processor, and uses XSLT stylesheets to transform the XML to user-presentable HTML and XML Schema to preserve the XML validity. A commercial version with table, rich text, and enumeration editing is available as well.
The edit-on JavaBean SDK is a customizable, feature-rich JavaBean that allows developers to add WYSIWYG editing functionality to their AWT- or Swing-based applications. It features an intuitive word processor-like user interface that enables XHTML content authoring with XML markup, and has a royalty free run-time license.
XWidglets is a complete rich Java Swing tool for designing, creating, and using XML-based GUIs. It provides a lightweight XML client, clear separation between view, data, and process, MVC I and II support, event management, a consistent look and feel across platforms, a rich set of GUI components, and n-tier architecture integration.
The Orangevolt XSLT Plugin for Eclipse provides XSLT support to the Eclipse platform. It is the Eclipse-based successor of the Java/Swing-based ROXES XmlWrite XSLT editing environment. It provides many great enhancements when working with XML inside Eclipse. It implements XSLT launch configurations, XML editor enhancements, configurable XML outlines, an xpath navigator view, and more.