xmlroff is a fast, multilingual, multi-platform XSL formatter that transforms XSL-FO documents (or any XML with an appropriate XSL stylesheet) into PDF or PostScript. It aims to excel at DocBook formatting, and it integrates easily with other programs and with scripting languages.
RefDB is a reference database and bibliography tool for SGML, XML, and LaTeX documents. Command-line tools allow interactive or scriptable access to the data which are stored in a SQL database. RefDB can also be accessed through a Web interface, a SRU interface, or via editor extensions (Emacs/vim). Libraries for Perl and PHP are available for programmers. RefDB provides sophisticated character encoding handling, using Unicode by default.
The XCB library provides an interface to the X Window System protocol, designed to replace the Xlib interface. It has several advantages over Xlib, including size (small library and lower memory footprint), latency hiding (batch several requests and wait for the replies later), direct protocol access (one-to-one mapping between interface and protocol), thread support (access XCB from multiple threads, with no explicit locking), and easy creation of new extensions (automatically generates its interface from machine-parsable XML protocol descriptions). Xlib can also use XCB as a transport layer, allowing software to make requests and receive responses with both, which eases porting to XCB. However, client programs, libraries, and toolkits will gain the most benefit from a native XCB port.
lxml is a Python binding for the libxml2 and libxslt XML processing libraries. It aims at ease of use of the API for Python programmers and exposing the many libxml2 features. It implements the Python ElementTree API on top of libxml2. It extends this with support for XPath, XSLT, Relax NG, XML schema, and more.
The GCC XML Tree Node Introspector project consists of a patch to the gcc compiler to output the internal compiler tree nodes in RDF/XML and programs to process that RDF/XML. The tree nodes are complex data structures which represent the source code inside the compiler. Through these tree nodes, users are able to extract information from their programs that would be otherwise very difficult to obtain. Modules exist to store these nodes in Redland RDF using a Berkley database. The long-term goal of the project is create a high-level API that will make the programmatic manipulation of programs easier than it is now.