* Invite anyone as a guest collaborator by email; they need not be a WordPress user on your website.
* Guest Collaborator will get an invitation with a temp passcode that will unlock the post (they are invited to collaborate) and can view it.
* Guest Collaborator will be able to see the post content (but can't edit) and can add comments, reply to comments and mention other authors in the content.
* Guest Collaborator will get an email notification when the author replies, resolves or mentions the guest collaborator in the comment.
* The administrator can see a list of all the Guest Collaborators and revoke their access to the posts.