Imagine an application with a UI somewhere between pidgin and phpbb, where you can add buddies to a buddy list. You can then arrange the buddies into groups however you like. If you want to make a post you can signal which of the people/groups on your buddy list should be able to view it, and include a 'suggested sub-forum' to aide in organization. You can then select any subset of your buddy list and communicate with them as if it were a forum. When your correspondents get the message from you, they can send the reply to the same group of people you sent the original message to, or any subset of the original group , provided your buddy lists are synched (otherwise you can send replies only to people who you actually know about who are also members of the group of people the original message was sent to, or subsets of it). Encryption of all communications is of course managed by the application, forward messages mixed through a distributed mix net and then received through distributed private information retrieval in fixed 'refresh' intervals.