I want to start a forum with 1 very specific requirement. Can you help me find one that will work?

I want to start a forum where the replies are only visible to the thread starter, forum staff (mods and admins), and maybe the person who posted the reply. I don’t want anyone else to be able to see replies.

Imagine like Craig’s List but instead of having to email the people it was all contained in a message board. I don’t want people to know how many others have replied to a topic.

I know I’ll probably need to modify the forum software somehow, which is just fine with me.