In the mid 1980s, an Italian designer named Alphonso Giambelli developed a bullpup pistol-caliber carbine with hopes of selling it to Italian law enforcement. That never happened, but the gun was offered on the commercial civil market as the semiauto AGM-1 by a company named Algimech (after ALphonso GIambelli). At least a handful of these carbines came into the US before the 1989 assault weapons import ban, chambered for 9mm Parabellum and 9x21mm. they were also offered in a variety of other calibers (.45 ACP, .45 HP, .22LR, .22 WMR) but it is unclear if any of those were ever manufactured.
The AGM-1 has an 18″ barrel and uses slightly modified Browning High Power magazines for both 9×19 and 9x21mm. The barrel is easily removed, and there is nothing particularly complex about its design.