An online forums consist of a board and lots of topics.
What would an offline version look like?
What if we do it in pen and paper. To start a new topic,
you get an empty journal with a wide spine. You write
the
topic on the spine, then you place the book on a vertical
shelf.
Books on
the top are the most recently written on, and
books on the bottom are the older ones.
---------
You could place such system anywhere on libraries,
toilets,
cafes. etc...
Oh, and best of all, it can survive without the internet.