TOPS filesharing is a disk sharing arrangement for Macs, PCs, Suns, and a couple of other late 80s - early 90s filesystems. The protocol on the wire is AppleTalk, usually on LocalTalk wiring with PhoneNet connectors and TOPS cards in PCs. Each TOPS init is serialized, so you will need at least 2 copies with different serials. TOPS was sold by Radio Shack under RS' own brand name and a couple of other companies sold it as well. Sometimes you can find these network dongles in junk piles, and they give you a way to connect vintage DOS PCs to vintage Macs. We used TOPS (Transcendental OPerating System) at Beck-Tech, Micah, and Nuvotech, and it worked pretty well, especially as it was the only common way to interconnect Macs and PCs at the time.

After Sun bought the company, development slowed and halted, and it faded away. The IP version is news to me. Interesting find.