Archive created by OpenSimulator, also known as "OpenSim," an open source 3D application server used for creating virtual environments accessible over a network; contains "prims," or items, and all asset data necessary to fully load the terrain, object textures, and their inventories on a different system.

OAR files can be created using the "save oar [filename]" command from the region console and can be loaded using the "load oar [filename]" command.