The M61 Vulcan 20 mm cannon is the most prolific member of a family of weapons designed by General Electric and currently manufactured by General Dynamics.
It is a six-barreled rotary cannon capable of more than 6,000 rounds per minute. Similar systems are available ranging from 5.56 mm to 30 mm (there was even a 37 mm Gatling on the prototype T249 Vigilante AA platform); the rate-of-fire being somewhat inversely-proportional to the size and mass of the ammunition (which also determines the size and mass of the barrels).
Another Gatling design well-known among aviation enthusiasts is the GAU-8 Avenger 30 mm cannon, carried on the A-10 Thunderbolt II (Warthog) attack aircraft, a heavily-armored close air-support aircraft. It is a seven-barreled cannon designed for tank-killing and is currently the largest bore Gatling weapon active in the U.S. arsenal.