Sigma Network

The Sigma Network (also known as Sigma for short) was a wide-area packet-switched network, and was one of the most successful online services prior to the World Wide Web. Developed in 1981 as the signature product of Korian technology company Protonetworks, with the intent of being useď for internal communication in Korian businesses.

Protonetworks reported that the Sigma Network had 8 million connections in 1996, with 6 million of those being located in Koria.

The Sigma Network specifications were published as open-source in 1990. Implementations are avaliable for Windows, Classic Mac OS, Linux, BSD, and TS-UGOS.

Services
Protonetworks hosted 4 official services on the Sigma Network, which were available in all regions with access to the Sigma Network: Other notable Sigma Network services included:
 * Comsend — Group communication
 * Imageland — Image sharing
 * Videon — Video sharing
 * Jiohieu — Virtual world and game creation

Software
The default "sigma" command to access the Sigma Network only has coloured command-line output. The name of the program being used to access the network is reported to the connected service, allowing Sigma servers to refuse the client access if the invalid software is used.