TOPS (Transcendental OPerating System) is a peer-to-peer LAN-based file sharing system best known in its Macintosh implementation, but also available for DOS and able to interoperate with Unix's NFS.[1] Originally written by Centram Systems West, the company was purchased by Sun Microsystems as part of Sun's development of the NFS ecosystem.[2] The Centram company was renamed to TOPS after its acquisition by Sun.[1] Sales of TOPS dried up after the introduction of System 7, which featured a similar file sharing system built-in, and Sun spun off their NFS developments to Sitka.