Symbian OS is a proprietary operating system, designed for mobile devices, with associated libraries, user interface frameworks and reference implementations of common tools, produced by Symbian Ltd. It is a descendant of Psion's EPOC and runs exclusively on ARM processors (while EPOC ran on x86 processors). EPOC first appeared in 1980 and was renamed to Symbian in 2001.
For more on this OS see http://www.symbian.com/symbianos/index.html
Symbian OS devices include the Psion5, Psion5mx, Psion Revo, Psion Revo+, and Diamond MAKO organizers. They also include the Nokia 9210 (European model), 9290 (American model), Ericsson R380, R380e and R380 Smartphones.