Answer by Jeff Hawkins:

This is reportedly the best Wiki Theme for WordPress. WordPress › My Wiki Theme
If you just need a wiki why not forgo WordPress for this and use instead Wikia – MediaWiki
If you'd like a blog with your Wiki (that would be a great idea in several ways) either build a Wiki and install WordPress in a sub-directory. That would give you the best of both worlds or else you could just use the  WordPress › Theme Directory " Free WordPress Themes and configure it to have a blog within the WordPress installation also.

What is the best WordPress theme for a wiki-like website?