TclXSLT [L1 ] is the XSLT accessory to the TclXML project. It wraps the GNOME libxslt [L2 ].
An example application using TclXSLT is tkxsltproc, a GUI for xsltproc. For Mac OS X and Windows at http://tclxml.sourceforge.net/tkxsltproc.html
In a separate but related project, Steve Ball is wrapping libxml [L3 ] with a TclDOM-compatible API. This package is called Tcldomxml (aka TclDOM/libxml2).
Note that TclXSLT requires Tcldomxml for its operation.
Steve Ball has a minimal example of how he calls back to Tcl to handle a common need for an external reference with TclXSLT [L4 ].
This package is part of the ActiveTcl Batteries Included distribution.