Not a specific family history Wiki, but there is rootsweb (and others) with specific family interests as you probably already know.
You might want to look at LifeLines, http://lifelines.sourceforge.net
. You can import GEDCOM files, create reports, etc., etc. There are a couple of Java-based applications that are getting there if you look around -- I seem to remember one that let folks from the outside world access (sorry, I don't remember what it is; Google is your friend).
Give some thought to starting your own Wiki -- you can get the software, build and install it, and roll your own Wiki.
Go look at http://www.mediawiki.org/wiki/MediaWiki
, which is the software for Wikipedia that you can download and install on your own system and set up a Wiki for whatever purpose you may have in mind.