Window System X
June 19, 1984 – “Window System X” (what we now usually call “X Windows”) was announced to the world in an email from Robert Scheifler. “I've spent the last couple weeks writing a window system for the VS100. I stole a fair amount of code from W, surrounded it with an asynchronous rather than a synchronous interface, and called it X,” Scheifler wrote in the email, concluding with, “anyone who wants the code can come by with a tape.” This system has undergone many changes over the years, but has proven to be critically important.
Fun Fact: The W Window System ran on the V Operating System. So V ran W, whose code was stolen for X.