I'm reminded of a tactic I implemented in a group context I had some control over once: discussion was mediated by each speaker getting to speak uninterrupted until they were done and then handing the floor explicitly to another member of the group, and everyone (~100 people) was issued four index cards (Red, Green, White, Blue) with instructions to raise them to indicate the following:
Red = disagreement
Green = agreement
White = boredom/disinterest
Blue = confusion/request for clarification.

It wasn't a particularly good mechanism for mediating discussion, but I was intrigued by the ways people differed in terms of their response to various response patterns.