There are many players in the world of semi-automatic shotguns.  The big name that stands out among the rest is Benelli.  They have a well earned reputation among the shooting community as one of the best.  Other companies such as Remington, Mossberg, and even the Saiga have become popular semi-automatic models. Most interesting is the popularity among the Saiga 12.  The Saiga 12 is a shotgun clone of an AK-47.  It uses all the same parts and design as the AK, but has been modified to allow the gas system to operate with shotgun shells.  Unlike Benelli, Saiga uses a box-fed or drum magazine.  They vary in capacity from 2 rounds to 20.  They are currently legal in California with some modifications.  The popularity of the Saiga 12 has brought many improvements and aftermarket accessories.  They also become popular among 3-gun competitors and clay shooters.