SHARE Inc. is a volunteer-run user group for IBM mainframe computers that was founded in 1955 by Los Angeles-area IBM 701 users. It evolved into a forum for exchanging technical information about programming languages, operating systems, database systems, and user experiences for enterprise users of small, medium, and large-scale IBM computers such as IBM S/360, IBM S/370, zSeries, pSeries, and xSeries.
A major resource of SHARE from the beginning was the SHARE library. Originally, IBM's operating systems were distributed in source form and it was common for systems programmers to make small local additions or modifications and to exchange them with other users. The SHARE library and the process of distributed development it fostered was one of the major origins of open source software.
SHARE was later incorporated as a non-profit corporation based in Chicago, Illinois and is currently located at 401 N. Michigan Avenue. The organization produces a newsletter and conducts two major educational meetings per year.
In September 1999, GUIDE International, the other major IBM mainframe users group, ceased operation. Although SHARE did not formally take over GUIDE, many of the activities and projects that were undertaken under the aegis of GUIDE moved to SHARE, and GUIDE suggested to its members that they join SHARE. In August 2000, SHARE took over the guide.org domain name.
Today, SHARE's membership of 20,000 represents some 2,300 enterprise IBM customers.