OpenServer, previously SCO UNIX and SCO Open Desktop (SCO ODT), is a closed source version of the Unix computer operating system developed by Santa Cruz Operation (SCO), later acquired by SCO Group, and now owned by Xinuos
SCO OpenServer 5, an AT&T UNIX System V Release 3-based operating system, was initially released by The Santa Cruz Operation in 1995. Based on SCO UNIX 3.2v4, SCO OpenServer 5 would become SCO's primary product and serve as the basis for products like PizzaNet (the first Internet-based food delivery system done in partnership with Pizza Hut) and Global Access (the first commercially licensed and bundled Internet Operating System). Due to its large installed base, SCO OpenServer 5 continues to be actively maintained by SCO with major updates having occurred as recently as April 2009.
For More on Open Server please refer : http://www.sybase.in/products/archivedproducts/openserver