Saxon-HE - put saxon9he.jar in /Library/Java/Extensions.
Apache XML Commons Resolver (download) - put resolver.jar in /Library/Java/Extensions.
java \ -Dxml.catalog.files=/etc/xml/catalog \ net.sf.saxon.Transform \ -x org.apache.xml.resolver.tools.ResolvingXMLReader \ -y org.apache.xml.resolver.tools.ResolvingXMLReader \ -r org.apache.xml.resolver.tools.CatalogResolver \ -o $OUTPUT_FILE.xml \ $INPUT_FILE.xml \ $XSL_FILE.xsl
Saxon-HE is a noncommercial version of the Saxon XSLT processor. The main (perhaps only) reason for using it instead of libxslt/xsltproc is that it implements XSLT 2.0.