Libxslt is the XSLT C library developed for the GNOME project.  XSLT itself is
a an XML language to define transformation for XML.  Libxslt is based on
libxml2, the XML C library developed for the GNOME project.  It also implements
most of the EXSLT set of processor-portable extensions functions and some of
Saxon's evaluate and expressions extensions.

People can either embed the library in their application or use xsltproc the
command line processing tool.

WWW: http://xmlsoft.org/XSLT/