Symbian OS
Symbian OS was the most widely-used smartphone operating system in the world until 2010, when it was overtaken by Android. Development of Symbian OS (operating system) was discontinued in May 2014.
Symbian OS began as an operating system called EPOC, which was developed in the 1980s by a company named Psion. In 1998, in a joint venture with telephone manufacturers Nokia, Ericsson, and Motorola, Psion became Symbian, Ltd., and EPOC became Symbian OS.
In 2008, Nokia acquired Symbian, and most of Symbian OS's source code was released under an open source license. At the time, it was one of the largest open-source code bases ever released to the public.
As of 2014, developers are no longer able to publish new Symbian applications, but existing applications are still available for download.