Open Space is an approach to help you put together self-organizing conferences. I was first introduced to it by Norm Kerth in 1997 and have since seen it used, and used it myself, many times. It seems to work well in small scales, groups of a dozen or two people, and at larger scales of one or two hundred. I've seen it for periods of one to three days. I'll describe it with variations I have seen: Crested Butte is a small annual workshop of around 20 people, Agile Universe 2002 had about 100 or so at the conference with Open Space in one track (they've continued to do this since, but I've not been able to get there), foocamp did this with a couple of hundred people. The technique was developed by Harrison Owen and is well described in his book.
The unusual (and powerful) thing about Open Space is that you don't pre-plan a list of activities and speakers. Instead you provide a basic skeleton of time and space, and the attendees figure out what actually happens. The result is a more participative and energetic event. (It's also less work to pre-organize, which I confess is an attraction to me ;-)
The skeleton of the meeting is the space/time matrix, or as I call it The Grid. It's a simple two dimensional table, one dimension being time slots, the other being spaces to meet. The spaces to meet can be quite informal, anywhere with a few chairs. For a dozen or two people I find four spaces usually are enough, and you'll mostly only use two or three of them. It's best when they are close enough to easily walk between them but far enough for loud voices like mine not to carry too much. At Agile Universe 2001 we had a very large room and set the spaces in the corners, at Crested Butte we use two rooms and a coffee shop. At foocamp there were a bunch of rooms of different size: a rough indication of size and whether it had a projector was marked on the grid.
I've tended to use one hour sessions, Owen prefers 90 minute sessions - either is fine. I do like decent breaks of 15 minutes or even half an hour between session to encourage informal conversation. A good way to seed a topic is to raise a question that needs to be addressed if you're going to be satisfied with the conference.
Get the grid drawn up before you start. I usually put it on several sheets of flip chart. The sessions themselves appear as post-it notes that fit into the cells of the table. At Agile Universe the grid was larger so that the cells were flip chart sheets. At foocamp people just wrote directly into the cells, although that causes problems when you want to move sessions so I prefer post-its.
When the conference starts you get everyone together in a one room, preferably in a circle, and explain how it all works. Then you invite people to convene sessions. Anyone can decide to convene a session, they do this by announcing to the group what the session is about and giving it a title which will go on the grid later. Continue to let people nominate sessions until the energy dissipates. You don't have to get all the sessions at the beginning, more will appear as the conference unfolds.
Once you have a bunch of sessions and conveners, then invite the conveners to schedule the sessions. To do this the conveners put their session onto a space on the grid. It's entirely up to the conveners as to what slot they put something in. Inevitably there will be clashes. People who want to attend two clashing sessions need to talk to the conveners of those sessions and persuade one of them to move time-slots. The final result is never perfect, but never worse than more planned approaches.
Once you have sessions on the grid, you then just let things roll. People can add new sessions to the grid at any time, and conveners may move their sessions at any time too (although it's not wise to move a session if it's in the very next time slot.) Typically people will look at the grid after each session ends to decide what to go to next, so make sure the grid is posted in a place that's easy to get to. It's useful to have people add their names to sessions they really want to attend, that helps conveners do the scheduling.
It's useful to get everyone together in the circle at intervals, say the beginning of each day, to announce new sessions and any other stuff.
If you want a record of the event, you can do this by getting each convener to write a summary of their session, these can then be combined to form a proceedings. Agile Universe did this on a wiki, which was alright - but I prefer the sound of Owen's approach. In this each convener writes up the session right away (and can be done in a wiki), but then prints out the summary and posts it on a visible wall. I prefer the idea of the wall because that way everyone can easily see it and it can spread discussion. Most open spaces I've done didn't involve proceedings, so I don't have much experience on this.
Owen describes the one law of Open Space is the Law of Two Feet: if anyone finds themselves in a place where they are neither learning nor contributing they should move to somewhere more productive. Essentially this means that movement between sessions is normal. If I find two clashing sessions I fancy, I'll spend some time in each. Many people find this unnatural, there's a belief that it's rude to move, but once you get used to open space then this movement becomes comfortable.
That's my brief description, there's plenty more information if you want to run this kind of event. Owen's book is excellent, if a touch Californian for my taste. There's also a web site in several languages.