As mentioned previously, the GNU project was started in 1983 as a response to the closed source software that was by then being distributed by most computer manufacturers along with their hardware. Previously, there had generally been a community that would share source code among users, such that if anyone felt that an improvement could be made, they were free to fix the code to work as they would like. This hadn’t been enshrined in any legally binding paperwork; it was simply the culture in which developers naturally operated. If someone expressed an interest in a piece of software, why would you not give him a copy of it (usually in source code form, so that he could modify it to work on his system? Very few installations at the time were sufficiently similar to assume that a binary compiled on one machine would run on another). As Stallman likes to point out, “Sharing of software…is as old as computers, just as sharing of recipes is as old as cooking.” 1
Stallman had been working on the Incompatible Timesharing System (ITS) with other developers at MIT through the 1970s and early 1980s. As that generation of hardware died out, newer hardware came out, and — as the industry was developing and adding features — these new machines came with bespoke operating systems. Operating systems, at the time, were usually very hardware-specific, so ITS and CTSS died as the hardware they ran on were replaced by newer designs.
ITS was a pun on IBM’s Compatible Time Sharing System (CTSS), ...