Germany
The Becker revolving shotgun is a unique firearm designed in Germany in the late 19th century and produced in the 1920s. It features a blow-forward action, where the barrel is pushed forward to cock the shotgun, and it holds five rounds in a six-shot cylinder, although only five are actually usable due to a design flaw. Only about 100 to 500 units were produced, making it a rare and interesting piece of firearms history. The shotgun operates by redirecting gases from fired shells to recock the action, and it lacks an external hammer for manual cocking.
US
The Roper revolving shotgun was an early cartridge-firing repeating shotgun that could carry and fire four rounds without reloading. It was offered in both 12ga and 16ga (this one is 12ga) and used a rather unusual open-bolt mechanism. Cocking the hammer fully would bring a shell into position between the bolt and chamber, and firing the gun would cause the bolt to drop forward, chamber the cartridge, lock in place, and immediately fire. Re-cocking the hammer would extract the fired case but leave it in the rotary magazine, and then bring a new shell into position to be fired. As a result, one could fire four rounds and then would have to unload the 4 empty shells form the magazine carousel before reloading… 
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