Symbian
Nokia, Motorola, Ericsson, Psion and others joined to create Symbian association. This let them promote using EPOC designed for mobile phones.  Symbian is a follower of EPOC system.  It is used in pocket PC Psion, running on the ARM processors.  This operating system has had many changes since it was first created.  Nokia smartphones are the major users of Symbian OS.