An Anti-Replicator gun (or ARG, for short) is a weapon designed to destroy the Asurans, a form of Replicators found in the Pegasus galaxy. It was designed by Lt. Colonel Samantha Carter, based on the disruptor technology designed by Colonel Jack O'Neill using an Ancient Repository of knowledge and put into mass production by the Asgard.
The ARGs, like the original Replicator disruptor, emit a directional energy pulse designed to disrupt the subspace link that allows Replicator cells to communicate, reducing the target to a harmless pile of individual cells. Unlike the original, the ARG has been scaled down into a much more compact design. It is built much like a small rifle, with the emitter placed at the end of the barrel. The emitter is also much smaller, being only slightly larger than an actual gun barrel would be. The weapon has a retractable stock, allowing it to be wielded either as a bulky pistol or with more precision as a rifle. Each ARG includes a control crystal that can be directly interfaced with Ancient systems, and can be used to apply the same disruptive properties to Ancient shield technology. (SGA: "The Return, Part 1", "The Return, Part 2")
Functionally, the ARG does not appear to have been altered much if at all from the original design. Though the Asurans differ in their construction, they still use a subspace link to communicate, which is what the device disrupts. The device is effective on both the original Replicators and the Asurans; though the one Milky Way Replicator it was tested on was immune, this is because it had been intentionally designed with an immunity to the weapon. Like the Milky Way Replicators, the Asurans were eventually able to develop an immunity to the weapon, and were able to do so much quicker than the Milky Way Replicators. (SGA: "Lifeline") (SG1: "The Ark of Truth")
A much larger satellite version of the ARG was also being developed, based on a Replicator disruptor satellite designed by the Asgard. It would have been capable of destroying Replicators on a planetary scale, vastly reducing the chances of a Replicator being able to adapt to the weapon. With their subsequent adaptation to the disruptor technology, followed by their destruction through alternate means, the likely development of the satellite became a low priority. (SGA: "First Strike")