A worker-owned consulting firm, basically. Also called a co-op. You get the benefit of shared clients and administration support, without working for "somebody else".
I don't know of any large ones, but I have seen quite a few around.
My experience is that 'collectives' aren't a lot easier for the socially impaired than traditional body shops, and they usually have less work.
they do usually charge a much smaller cut, though, which is pretty good, so if you get along with the people, and they do have work, they can be pretty great.
I don't think I'd advise anyone to rely on a collective as their primary income any more than I'd advise anyone to rely on a body shop as their primary income. Treat the job as a job, be open to jobs that don't go through your collective or body shop.
I don't know of any large ones, but I have seen quite a few around.