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.
Mughal Empire
Fathullah Shirazi (c. 1582), a Persian polymath and mechanical engineer who worked for Akbar, developed an early multi gun shot. As opposed to the polybolos and repeating crossbows used earlier in ancient Greece and China, respectively, Shirazi's rapid-firing gun had multiple gun barrels that fired hand cannons loaded with gunpowder. It may be considered a version of a volley gun.