I just wanted to write a mini-review of Mingle Forum - I think it is the best, and probably only reasonably well working WordPress forum plugin.
I wanted a simple forum for my site. A few months ago, I had looked at all the WP forum plugins, and could not find one that seemed to work right. So I put off adding a forum for a while until the need to do so became a real necessity.
So I first thought I'd use one of the standard PHP forums such as PHPBB or myBB or one of the many others. While there are many very nice forums out there, they all were really way more than I needed, and involved another piece of software to install and maintain. Plus, none of them would really integrate that well into my site.
So I decided to give the WP plugins another look. I'm glad I did, because I discovered Mingle Forum. It is a fairly small forum, and contains the basic features required of any forum, without too many options or maintenance overhead. It just plugs in to WordPress, and is up and working almost instantly.
That is not to say it is yet perfect. It still requires a bit of FTP magic to add new skins for it, for example. It's default skins are not yet compatible with Twenty Ten.
But what is great is that it is under active development, and I'm sure these small issues will be worked out very soon.
Once you get it set up, and looking like you want, it seems to be very functional with all the features you really want in a forum. It uses the built in WordPress user capabilities for registration, and will allow guest posts without registration.
And it looks good - either using a one-column, no sidebar page, or on a multi-column theme with a narrower space for the content.