Atlas' Portal Gun is a variant of the Portal Gun. It is the version used by Atlas, a sphere-shaped robot in the game Portal 2in co-op mode. Its counter-part is the P-Body Portal Gun, which was Atlas' partner in the extra Portal 2 co-op challenges. Its main use is to allow more than one system of portals in SMP. It can occasionally be found in dungeons.
The Atlas Portal Gun creates portals, which allow for same-dimensional transportation, regardless of distance. In order to make a link, Right-Click on the first location for teleportation, and Left-Click on the second location. Walking through the 2-Block rings will teleport you to the other one. In order to change one of the Rings, simply Right/Left-Click again. To reset both portals, press R.