The Phillips & Rodgers M47 Medusa is a mechanically very interesting firearm; a revolver that can chamber basically any cartridge with a 9mm bullet diameter and an overall length no longer than a .357 Magnum. This is made possible because a revolver does not have the headspace requirements of a semiautomatic handgun, and the barrel doesn’t know one type of bullet form another, so long as they are not larger than the bore diameter.
What makes it difficult, is finding a way to hold a variety of different cartridges properly in position for reliable firing and extraction. Jonathan Phillips solved this problem with his 1995 patent for the extractor mechanism that is the fundamental heart of the Medusa revolver. It uses long flexible fingers which snap into the extractor grooves on rimless cartridges or can be depressed down away from the cases of rimmed cartridges. These fingers allow proper indexing of virtually any cartridge that will physically fit. They are, however, also the weak point of the gun, as they are pretty much the only fragile component, and since the company quickly went out of business, replacements are completely unavailable.
In my shooting, I used .357 Magnum, .38 S&W, .380 Automatic, 9x20mm Browning Long, 9×19 Parabellum, 9mm Largo, 7.62mm Tokarev , and .32ACP. The last two obviously did not engage the rifleing as they are substantially smaller than the bore, but the fire safely regardless. The most significant question, of course, is how many people would actually have a need for such a system, beyond simply thinking it is cool (and if the multicaliber capability makes up for the finicky loading, extraction, and accuracy).
For a more detailed look at the history of the Medusa, I recommend this article by AirborneCombatEngineer.