OpenID can work with Wordpress & MediaWiki, so we're thinking about that as a backend.
I can't say I know of any measures, no. Would the other options work with your existing wiki login system? If so, I'll keep an eye on 'em and see if how they work for you...
Interesting, thanks - but there are no anti-spam measures, right?
We want to try out a couple of forum options (Wordpress plugin, and Wordpress-compatible forum) but exploring all the options...
Actually, there has been no prob at all with spam on there...