I'm looking for a solid open-source commenting engine written in PHP. It needs to have workflow/moderation capabilities as well.

I've checked into Disqus, and while I like the concept, the site owner's may develop their own login system at a later point, which would have to integrate with the comment system. Also, I'm not sure that they want the comments hosted remotely.

Does anyone have any recommendations that I might look into? Alternatively, if you have experience with Disqus, what do you like/dislike about it?