Volley gun
The Ribauldequin was a medieval version of the volley gun. It had its barrels set up in parallel. This early version was first employed during the Hundred Years' War by the army of Edward III of England, in 1339. Later on, the late Swiss army employed it.
Revolver
In the U.S. the traditional single-action revolver still reigned supreme until the late 19th century. In Europe, however, arms makers were quick to adopt the double-action trigger. While the US was producing weapons like the Model 1873, the Europeans were building double-action models like the French MAS Modèle 1873 and the somewhat later British Enfield Mk I and II revolvers (Britain relied on cartridge conversions of the earlier Beaumont–Adams double-action prior to this). Colt's first attempt at a double action revolver to compete with the European manufacturers was the Colt Model 1877, which earned lasting notoriety for its overly complex, expensive and fragile trigger mechanism, which in addition to failing frequently, also had a terrible trigger pull unless given the attentions of a competent gunsmith.
In 1889, Colt introduced the Model 1889, the first truly modern double action revolver, which differed from earlier double action revolvers by having a "swing-out" cylinder, as opposed to a "top-break" or "side-loading" cylinder. Swing out cylinders quickly caught on, because they combined the best features of earlier designs. Top-break actions gave the ability to eject all empty shells simultaneously, and exposed all chambers for easy reloading, but having the frame hinged into two halves weakened the gun and negatively affected accuracy, due to lack of rigidity. "Side-loaders", like the earlier Colt Model 1871 and 1873, gave a rigid frame, but required the user to eject and load one chamber at a time, as they rotated the cylinder to line each chamber up with the side-mounted loading gate. Smith & Wesson followed 7 years later with the "Hand Ejector, Model 1896" in .32 S&W Long caliber, followed by the very similar, yet improved, Model 1899 (later known as the Model 10), which introduced the new .38 Special cartridge. The Model 10 went on to become the best selling handgun of the 20th century, at 6,000,000 units, and the .38 Special is still the most popular chambering for revolvers in the world. These new guns were an improvement over the Colt 1889 design since they incorporated a combined center-pin and ejector rod to lock the cylinder in position. The 1889 did not use a center pin and the cylinder was prone to move out of alignment.