Nothing. I saw this on missile technology back in the early 90’s.
In the first attempt to bring the first stage back, the rocket went into a severe rotation. Spacex figured it would get better when the landing legs were attached, but these are also an extra addition to control the spin.
These gridded fins were used many years ago in missile technology. This is the exact same configuration as the ones I remember but used on the rear for guidance and stability. I though they were innovative the first time I saw them. Looks like borrowed tech to me now, lol.