Smoothbore .22 caliber arms were fairly common, sold for the indoor skeet games and for short range pest use. Another fairly common example was the 9mm "garden guns", smoothbore barrel using a 9mm shot cartridge (mostly European, but a few appeared on the US market).
Trappers used shot cartridges for dispatching smaller animals. Annie Oakley achieved considerable fame using a Marlin lever-action rifle shooting aerial targets while using .44-40 shot cartridges.
Haven't seen much in this line over the past few decades. Still see .22 LR and .22 Magnum shot cartridges, and a few handgun calibers (.38 Special, .357 magnum, few others) are still around. Those of which I am aware are intended primarily for use in standard rifled rifles or handguns; haven't seen any dedicated smoothbores for years (probably a problem for handguns due to GCA-68 shotgun restrictions).