The lxml XML toolkit for Python
Fast XML parser library in C
X3D is the open-standard format for 3D graphics scenes on the Web.
XMLJ is a Java XML Editor and validator project.
Dynamically loaded extension libraries for GNU AWK
EasyML serialization library, to and from XML, similar to Gson
C++ library for creating XLSX files for MS Excel 2007 and above.
eXist-db is a feature rich Open Source native XML database
Simple, lightweight XML parser in C, statically or dynamically linked.
Simulatoralive's Java libraries and programs
NO LONGER MAINTAINED
Minimalistic NCL (nested context language) implementation.
File validation and characterization
A library to convert between braille and MathML
xslet project provides some XSL libraries and applets.
This program allows embedding books in fb2 format in one, super-book.