Thinking about how to organize a workshop with NYC's urban farmers and gardeners, Phil Silva told me about "open space technology" that predates Bar Camp and the tech version of unconferences. In an open space technology experience, people are working towards solving a problem or answering a question -- it's productivity based, not just "birds of a feather" type sessions or presentations of work done that relates to the conference theme. In open space technology everyone tackles issues that are part of the same overarching issue. Open space technology emphasizes not only setting the agenda, but within each session, collaborating on the shared goals that were established at outset. It's about getting work done together, and an "unconference" may or may not be about that. Basically, adds a facilitation overlay to what i have known as an un-conference.
I think Public Lab's last Barnraising (Cocodrie 2012) was in fact conducted in this model, so I'm glad to learn about this precedent.
Wikipedia article on Open space technology