OD is a file format used by Mascopt, a professional network optimization tool. Single OD files contain graph used during network analysis processes.

Mascopt is an open source application written in Java that supports XML data standard. Files with OD are seldom encountered as the software that uses them is considered niche. Although Mascopt is distributed under LGPL license, since 2005 no new version had been released (the latest version is designated 1.3).