A file with .oar extension is an archive file used by the OpenSimulator application which is an open-source 3D application server for creating a virtual environment accessible to multi-users over the network. The OAR file format provides necessary asset data required to fully load the terrain, object textures, and inventories on a different system. OpenSimulator also has optional hypergrid that allows users to visit other OpenSimulator installations across the web. OAR files have internet MIME type application/oar and contains one or more archived files.
OAR File Format
OAR are binary files that are stored in compressed archive file format. The latest version of OAR file format is version 1.0 that has major changes from its previous version 0.8. The latest version supports storing multiple regions in a single OAR and is not backwards compatible with versions of OpenSimulator before 0.7.5. An OAR file is a gzipped tar file (tar.gz) in the the original unix tar format (not USTAR).
OAR Regions Example
AOR files can contain multiple regions. The structure of the archive is as follows (this example contains 4 regions):
The archive control file contains a major version number for defining compatibility with future format changes. The presence of assets in an OAR format is indicated by the boolean element <assets_included>. Information about the included regions is contained in a manifest that is present in the control file. An example of Archive.xml is as follow.