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.
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.
XIST is an extensible HTML and XML generator. It is also an XML parser with a very simple and Python-esque tree API. Every XML element type corresponds to a Python class, and these Python classes provide a conversion method to transform the XML tree (e.g. into HTML). XIST can be considered 'object-oriented XSLT'. XIST also includes a cross-platform templating language, Oracle utilities, and various other tools.
DOMC is a lightweight implementation of the Document Object Model (DOM) in ANSI C as specified in the W3C DOM Core Level 1 recommendation. When coupled with the Expat XML Parser Toolkit, DOMC can load, store, build, and directly manipulate XML documents represented as a tree in memory.
XML Binary Infoset Encoding (XBIS) is an encoding designed to eliminate most of the padding of XML text documents being passed between programs, while being faster to generate and interpret. The focus is more on speed than on size, so if document size is the major concern standard compression algorithms can offer superior results. The current Java implementation shows 4-8X performance benefits over standard XML parsers over a range of document types and sizes and across JVMs tested.