http://fxsl.sourceforge.net/
http://www.exslt.org/
these are complimentary. Fxsl implements functions in xslt, exslt
defines a list of functions and implementation guidelines so that one
can have extention functions not otherwise in the core. Saxon and if I
remember correctly Xalan both implement the exslt core functions.
XSL-List info and archive: http://www.mulberrytech.com/xsl/xsl-list