I would like to draw attention to George at www.limpidsoft.com. It is
small and pretty fast and, as far as I know, compliant with all of the
W3C XSLT 1.0 recommendatio. It is presently available only for Linux/Unix.
George is based on the Limpid XML library, which implements W3C DOM
(level 2 core), XPath 1.0 and XSLT 1.0.
Both George and Limpid are released under the GPL and are available for
free download.