On the subject of special extractor stars, there's the Philips & Rodgers M47 'Medusa', which is quite an unusual revolver.
On the surface, it looks like any other hand ejector double-action revolver you've ever seen (it's straight up based on a Smith & Wesson), it has such a previously mentioned extractor star assembly, an unusual kind where there's a springloaded tab/finger for each chamber, which can grab onto the rim of a rimless cartridge and hold it in place, without needing clips or anything.
The purpose of this here is to allow you to chamber and fire literally whatever cartridge which can fit and which fires a bullet which is .357 caliber or smaller in diameter, you can drop typical .38 Special and .357 Magnum cartridges into the chambers and they'll sit on top, but if you were to load 9mm Luger, 7.62mm Tokarev, or 9mm Steyr in there, they can be held onto by the extractor assembly, and they will be fired.
A double tapered forcing cone is intended for trying to solve issues of accuracy, but it seems to not work out all that well for shooting just normal .38 Special or .357 Magnum, while for much smaller caliber cartridges like 7.62mm Tokarev or even .32 Auto, it will obviously do nothing, the bullet will just glance, bounce and skid down the bore, and likely at pretty modest velocities compared to normal guns in those calibers, as the cases aren't properly enclosed and will generally rupture, allowing a lot of pressure to escape prematurely.
The company advertised that it was capable of chambering and firing a few dozen different cartridges, but it can actually shoot well over a hundred kinds.