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.
Sablotron is an XML toolkit which implements XSLT, DOM, and XPath. Sablotron is written in C++, and it can be used from C, Perl, Python, PHP, ObjectPascal, and via a command line interface. It supports the XSLT 1.0, XPath 1.0, and DOM Level 2 W3C specifications. It is designed to be as compact and portable as possible, and is maintained as an Open Source project by Ginger Alliance.
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.
Raptor is a C library providing a set of parsers and serializers for Resource Description Framework (RDF) triples by parsing syntaxes into RDF triples and serializing triples into a syntax. The parsers support RDF/XML, N-Triples, GRDDL, and Turtle, and via RSS tag soup: XML RSS, Atom 0.3, and Atom 1.0. The serializers support RDF/XML (3 flavours), Turtle, DOT, N-Triples, RSS 1.0, and Atom 1.0. Raptor handles RDF/XML as used by RDF applications such as RSS 1.0, FOAF, DOAP, Dublin Core, and OWL. It can use either expat or libxml2 for XML parsing, libcurl when available for URI retrieval, and is portable to many POSIX systems.
XML-Lit is a simple program to perform very basic literate programming with any XML-based markup language. It uses James Clark's Expat XML parser to weave (convert to a form suitable for processing) and tangle (extract the source code from) your XML documents. It has only been tested with DocBook at the moment, but there is no reason why it should not work with any arbitrary XML markup.
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.