XeTeX (by Jonathan Kew) is a successor to the shareware TeX/GX
program. It is a Unicode-based (UTF-8) TeX implementation which
is able to make use of Mac OS X AAT (Apple Advanced Typography)
.dfonts and OpenType fonts. It uses Apple's Quartz system
(which facilitates the afore-mentioned font access) to generate
PDF output.
XeTeX requires Mac OS {X} 10.3 "Panther" or later (although there has been some success using earlier versions). It is especially oriented towards multi-lingual typography, taking advantage of Apple's keyboard input systems and system font support for various languages.
The system is able to make use of Gerben Wierda's TeX facros/latex/contrib/wordcount (gzipped tar, browse)
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=wordcount