Microsoft bought a license to Version 7 Unix from AT&T. They mixed in some BSD stuff. Santa Cruz Operation (SCO) was originally one of the licensees of Xenix and ended up inheriting it from Microsoft around 1987.

SCO bought Unixware and some licenses for SysV from Novell. They ended up selling all that to a Linux and DOS vendor named Caldera. SCO ended up changing their name to Tarantella.

Caldera changed their name to The SCO Group and under the leadership of Darl McBride, they became one of the most annoying patent trolls ever.

Good point.

In any case, they sold it and it was called Microsoft Xenix.