SCO at one time stood for Santa Cruz Operations. I believe that, over time, that meaning of the letters has been deprecated and the company is know known by its initials.
Many years ago, SCO produced a product called Cisual Tcl which was a toolkit which attempted to provide one interface that would work either with GUI or CUI type applications.
DKF: Currently (late summer 2003) appears that the company known as SCO are committing corporate suicide by taking on COMPANY: IBM.
ZLM: The former SCO now has another name: Tarantella. Linux vendor Caldera bought their Unix division and changed its name to "The SCO Group".