The standard skeet gun is an over/under break action that has screw-in chokes. This configuration is available in just about any gauge from the smallest .410 to the largest 12-gauge.
Some shooters prefer to use a semi-automatic for skeet, also with screw-in chokes.
Either configuration works fine. The most important aspect of a good skeet gun is not the number of barrels it has or its action: it’s the balance and feel of the gun that allows you make smooth swings to hit the crossing targets of most skeet stations.