August 20, 2009, 8:23 PM — If I asked you to tell me the first software that was made available as open source, you probably would point to something that came out of ARPAnet, such as TCP/IP; I dare say you would at least mention one of the fundamental pieces of the Internet. But I gently brushed against an earlier computing endeavor that might qualify as the first open source application: IBM's Airline Control Program, or ACP. If ACP was not among the first open source apps — assuming we use the definition, "of or relating to or being computer software for which the source code is freely available" — then it was certainly an influence. Yet, in my old fuddy-duddiness, I'm surprised by how few people actually know ACP even existed. Especially since I think a few tendrils of its source code helped you make it onto your airplane flight today.
[ See also: Convincing the Boss to Accept FOSS ]
I do not promise that this is an authoritative history of ACP; I don't have enough data for that, and most of what I can find online about the software is written in technical jargon and old-style IBM-ese. I half expected to find a mostly-blank web page that says only, "This page intentionally left blank." Or left-justified. Whatever. What I impart here is primarily from my memory, since I was (and am) married to someone who worked with ACP peripherally in the early 1980s, when it was still going strong. I'm sure others will correct me on both technical and process points. Please try to avoid the expression of too much pleasure as you rudely put me in my place? Thanks.
Anyway: the early ACP was an operating system to manage reservations for airlines and other businesses that relied on reservations (such as hotel chains). This was among the earliest definitions of business mission critical software; if a reservations system went down for an hour, the hotel chain was probably out of business. It dated from about 1967.