Skydoc listed most if not all the brands who make similar products. If you go to TrueTrack's website they give a good explanation of what these things do.
If you have an older bike, like my 1990 FLHS, there are not many of these things available. I fitted a TrueTrack Tracula kit and it is brilliant! A Harley specialist who rode it recently reckons mine is the best handling dresser he has ever ridden. Not bad for an 18 year old bike!
On rubber-mount Harleys the rear wheel and swingarm are attached to the back of the gearbox. Buells and modern Sportsters have three stabilizer links, one at the cylinder heads, another in front of the engine, the other by the gearbox. The rubber mountings let the engine vibrate, while the links prevent the rear wheel moving sideways in the frame, such as when cornering.
Dressers have only two stabilizer links, one at the heads, the other in front of the engine. Dynas have only one link, at the heads. Softtails don't need stabilizers, as their engine is bolted in as god intended!
So these kits provide dressers with a third stabilizer. The improvements they give are worth the few bucks they cost and greatly improve handling. I have also fitted a kit to my wife's Dyna, with remarkable improvements.
I only have experience of TrueTrack. There is plenty of choice of brand, but what I will say is if you own a dresser, buy and fit one soon and don't look back!