The LensBaby composer is a lens mounted on a ball and socket arrangement which you can twist to change the way that it focuses the light onto the camera sensor.
I bought one a while back and every now and then I get it out and have a play. It is quite fun. Very old school, in that it is basically a single lens in a sliding tube. There is no auto focus and you adjust the aperture (the size of the hole the light comes through) by dropping in and out little metal masks that are held in place with magnets. A bit fiddly to use, but the lens itself is pretty darned sharp, and you can get results that would be very difficult to get any other way.
If you have a digital SLR and you fancy spending some time doing things the hard way, and never being quite sure how the pictures will come out, they are kind of fun.