I mean, there are open things about it. As in - TCP/IP is open. APIs to develop Windows programs are open.
In the same way as Solaris, HP/UX, Digital Unix and something else were open. Except Sun would even send OS sources in addition to documentation to customers interested in optimizing something they'd do, or so I've heard.
But the "most open" thing looks like 2003 "get the facts" style propaganda, except back then they had technical competencies, now it's purely the oligopoly.
But the “most open” thing looks like 2003 “get the facts” style propaganda, except back then they had technical competencies, now it’s purely the oligopoly.