Just c-pasting some very sound ideas of @Filip F from “Hello” thread here.

“Add a shoutbox. It is a place on the site where you can send small and quick messages and everyone on the forums sees them and can reply, without refreshing the site. It is something like a group chat on facebook, but everyone can talk.

Add Private Messages. This would be a great way how to communicate with other members, users could also disable their PMs if they do not want other users messaging them.

Make replies automatically quote the person, it will be much easier to see who is replying to who.”