UNIX is a big deal. It's one of the most influential programs in history. Most operating systems that we use today can trace their lineage back to UNIX. The only notable exception at this point is Windows. But all these new-fangled operating systems aren't blood relatives of UNIX, they are all derivatives. Second cousins, if you will. So how did we get from UNIX into a diverse field of UNIX-like things? It all starts with a little project at UC Berkeley.   Selected Sources:   https://archive.computerhistory.org/resources/access/text/2022/06/102743073-05-01-acc.pdf - Oral History of Bill Joy   https://archive.org/details/aquartercenturyofunixpeterh.salus_201910/page/n157/mode/2up?view=theater - A Quarter Century of UNIX