Imageboards?

* Threads are sorted by bump order.

* Posts can include images. Opening posts must include images.

* To reply to a post, you link the ID.

* Hovering over an ID displays the post, and each post also links to its replies.

* No identities.

* Dead threads get deleted.

* Threads automatically refresh every 15 seconds.

It encourages a more fast-paced discussion, which is very conversational and often nearly live.

EDIT: Also trollboxes; like a cross between IRC and guestbooks.