you are probably referring to the Alpine Trekker, made by BCA. They convert your alpine bindings to a randonnee binding- sort of. you clamp your boot into the frame using a system just like a step in crampon binding. The frame is on a hinge at the toe, allowing you to skin uphill like with randonnee bindings. The trekker then clicks into your binding. However, unlike randonnee bindings, you must get out of the Trekkers to ski down- you can't lock down the heel. They weigh about 2 1/2 lbs per pair, too, and give you a fair amount of lift.
I bought a used pair really cheap this season, anticipating a back country trip I never got to take- hope to try them next season or late this season.
Look here for more information BCA web page