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.
The goal of Hilbert II, which is in the tradition of Hilbert's program, is the creation of a system that enables a working mathematician to put theorems and proofs (in the formal language of predicate calculus) into it. These proofs are automatically verified by a proof checker. Because this system is not centrally administered and enables references to any location on the Internet, a world wide mathematical knowledge base could be built. It also contains information in "common mathematical language".
doclifter helps with lifting documents with nroff markup to XML-DocBook. Lifting documents from presentation level to semantic level is hard, and a really good job requires human polishing. This tool aims to do everything that can be mechanized, and to preserve any troff-level information that might have structural implications in XML comments. TBL tables are translated into DocBook table markup, PIC into SVG, and EQN into MathML (relying on pic2svg and GNU eqn for the last two).