From Wikipedia:
A strut bar, strut brace, or strut tower brace is an automotive suspension accessory usually used in conjunction with MacPherson struts on monocoque or unibody chassis to provide extra stiffness between the strut towers.
It's basically a thick rod that runs betweens the tops of the strut towers and is supposed to increase rigidity of the frame in turning. Some claim they do basically nothing on the already rigid Gen 3s as opposed to Gen 2s perhaps. But others say they help. Someone used to sell them a bunch of years back; I figured somebody may have one from their old Bull or something