Answers: http://wikia.com is a hosting service for wikis using the MediaWiki software that Wikipedia uses. You could just procure your own webhost and install MediaWiki if you like. It is free and all right documented.
http://www.wikidot.com/
www.pbwiki.com
If your hopefully techie enough, you can use Mediawiki (
http://www.mediawiki.org/) to trademark one like wikipedia.