THEOS, which transcribes to "God" in Greek, is an operating system which started out as OASIS, a microcomputer operating system for small computers that use the Z80 processor. Originally written in the late 1970s by Timothy S. Williams as a low-cost alternative to the more expensive mini- and mainframe- computers that were popular in the day, OASIS provided time-sharing multiuser facilities to allow several users to utilise the resources of one computer. Similar in concept to MP/M or UNIX, THEOS uses external device drivers rather than a kernel, allowing it to be more portable to other environments, though support has been primarily directed towards industry-standard hardware (i.e. PC's). THEOS is specifically aimed at small business users, with a wide range of vertical-market applications packages being developed and supported by individuals and companies.
A number of security features exist, including dynamic passwords (where the password includes part of the date or time, or client IP address, or other dynamic elements), allow/deny security, a comprehensive inbound and outbound firewall, and an option to require a certain level of encryption in the workstation connection. In addition, the object file format is proprietary, and the operating system uses Intel "protected mode" to further increase defence against buffer overrun attacks.
THEOS was introduced in Europe by Fujitsu and other hardware manufacturers 30 years ago, and is distributed by a number of distributors in Great Britain, Spain, Portugal, Germany, Italy and more. The 'current' version is THEOS Corona Commercial Release 6, which was released in December 2008, and a number of updates have been released since that time. The current Windows Workstation Client (as of May 2009) is version 3.16 from July 2003.