We had several of these around the New Orleans area during the first year after Katrina. In each case, teams of volunteer architects and city-planners came from around the country for a couple of weeks, set up a shared workspace, toured a particular devasted area, came up with ideas for rebuilding, and worked up drawings, etc., for slide-show presentation to the public.

After a couple of days working among themselves to create an introductory presentation, the public was invited to come see the proposed rebuilding options and provide feedback. The team would take this new information into account, make revisions while also working up new proposals incresing the scope of the overall project, and prepare another presentation (typically, two evenings later.)

The charrette that I attended lasted about 10-14 days, with public meeting/presentations every other weeknight. The meetings were in a large church, and the team of visiting professionals had their workspace in the adjacent school. We (of the local populace) were invited not only to the formal evening presentation/discussion meetings, but also to drop in during the daytime to observe and discuss the actual working of planning, etc.

In our part of town, the net result was a highly detailed document outlining a fairly ambitious vision of a better-than-ever rebuilt community. Now, two-and-a-half years later, it has become clear that many of the more ambitious aspects of the plan are not going to happen, but many ideas that came out of the exercise have influenced actual rebuilding that has taken place ~ especially work that could be done by individual property owners on their own homes and businesses. (Those aspects of the overall vision that would require action by city or state government were less likely to occur in real life.)

The final document from our charette in the Gentilly neighborhood was posted on the web as a book-length PDF file, as was a similar document that resulted from an earlier charette in suburban St. Bernard Parish. I don't know if these documents are still available ~ I'll go look, and post links here if I find anything.