It might be helpful to know how you want them to have a conversation. Through posts? Through comments? It might be helpful to know how you want them to have a conversation. Through posts? Through comments?
Since my aim is to hide conversation between selected Writers, the base is not important. It can be posts and comments, or a seperated table.
If these tools had the something like I wished, that could be nice:WP Admin Microblog or User Messages
What are they? You don't really want a forum, so if we knew what some of these were, we might know of or be able to find something similar.
They usually called "bridge". On some sites I have read that bridges doesn't work properly on next versions of forums or wp.
So as you tell free or paid, if not under development they will fail to handle their tasks.
To be honest, I think you want a forum, but with a plugin that can hide subforums from everyone but selected members. There is such a plugin for the stand-alone version of bbPress, but I'm not so sure about the plugin version.
Thanks for the trick. I will search for it. What bbPress make me think of is, I won't find the right or updated plug-in in the case of further need.
I have known and setup for friends twice bbPress and aggree with this page : Why I Didn’t Choose bbPress
Anyway thank you, I will write down my choose.