ARCNET (Attached Resource Computer NETwork) is a local area networking technology developed by the Datapoint Corporation around the same time as Ethernet. ARCNET is essentially the third-place contender in the LAN wars that were started in the 1970s. Ethernet was obviously the winner, IBM's token ring was second place, and ARCNET came in a distant third.
ARCNET uses a token bus scheme where a single token is passed around, and must be acquired by an individual station before transmitting. The bus topology is often advantageous because it does not require hubs (Ethernet) or a looped connection (token ring). The main advantage of the token bus is that communication latency can be guaranteed to be within certain bounds, as opposed to Ethernet which will take longer and longer as the network saturates.
John Murphy was the chief architect of ARCNET. The original vision was a distribution of local computers acting together as one; kind of like a cluster, before that term was coined. The original speed was 2.5Mbps, chosen to match the company's disk speeds at the time, but was later updated to 10Mbps. Although originally built for office networking, it has largely lost that battle and now exists primarily in industrial applications where real-time communication is needed. The ARCNET Trade Association (http://www.arcnet.com) is responsible for ARCNET advocacy.