From LQWiki

In the late 1960s, AT&T Bell Labs, MIT, and General Electric collaborated on a computer called the GE-645. The GE-645's operating system was called MULTICS (Multiplexed Information and Computing System). MULTICS really is the ancestor of all of the asynchronous time sharing systems common today. That list includes, but is not limited to, UNIX, BSD, Linux, and Windows.