'plug'

a child can be most creative if you provide him a bouncing ball of all things as the child can see endless possibilities emerging from such basic objects.
'LEGO' i feel has captured this essence. the fixturing system resemble the way one would use LEGO; in essence this system has a perforated panel onto which a given set of fixtures can be mounted as one fancies. also the look of the store can be changed just by rearranging these fixtures without much trouble.