Small mating hives made from expanded polystyrene foam, that contain small moulded plastic frames.
This type of nuc is very popular, it is however very light in weight and will blow about in the wind, but it can be strapped to the branches of trees using sections cut from car inner tubes. (Use thick, strong, branches with little or no movement.)
Note the recesses in the sides of the moulded plastic frame top bars are for queencell insertion. And the feeder at the rear of the frames.
I have never owned any of this particular type of mating hive, but I have experienced their use. I have recently revised my ideas and now prefer slightly larger mating colonies than can be contained in this type of box.
Albert Knight of BIBBA has had similar thoughts on size and has developed an adaptor board that will allow two or more of these boxes to be used together in a two or three storey configuration.