Basically they
1. put a high gloss polish on most balls, and
2. contain a substance that partially clogs the "pores" of resin balls, reducing (but not eliminating) the coverstock's ability to absorb oil. (As far as I know, a resin ball's hook capability is governed a great deal by its ability to rapidly absorb oil.)
The 3 main ones of which I am aware, Powerhouse Delayed Reaction, Neo-Tac Control-It and Valentino's UFO, use 2 different "slip agents". UFO uses what is termed an organic agent; I believe but do not know for certain that the other two use silicone. UFO's agent lasts about 25 games and can be easily removed with a mild or fine abrasive like a 4000 grit pad. The other two last much longer and need a rougher abrasive to remove the slip agent, like a 360 or 500 grit pad. All three (in my personal experience) need at least 2 good, solid, separate coats to insure an effective coating.