QNX cant be a result of symbian since it is 20years older than symbian and completely different.
http://en.wikipedia.org/wiki/QNX
RTOS cant be a os since it is a definition.
http://en.wikipedia.org/wiki/Real-time_operating_system

Also linux, bsd and qnx has their roots in unix, which inturn has its roots in multics. http://en.wikipedia.org/wiki/Multics
also, win 1,2 and finally 3 to 3.11 and windows for workgroups, are very different from winNT but also predates winNT. OS/2 should also be there since winNT=os/2 ver3.