I've seen that wikipedia runs on a 1.6devel
version of mediawiki.
(see
http://en.wikipedia.org/wiki/Special:Version )
Although I tried to open my eyes I couldn't find the files for any
1.6 version on
http://sourceforge.net/project/showfiles.php?group_id=34373#files nor
http://www.mediawiki.org/wiki/Download