Cat Trax are big bar-bell shaped wheel sets, used for moving catamarans around on the beach. It's lot easier (and gentler on your hulls) than dragging the boat across the ground, especially if there are rocks, concrete or soft sand.
There are different brands and styles, soft rubber wheels, hard plastic wheels; some even have dual sets of wheels, some have cradles for the hulls, some have a T-handle for better control. Nicer ones cost more, but cheaper ones still work.
Some folks make their own, because they can be pretty pricey.
What - Me Worry?
2006 Hobie Wave