Penny's OS 2.0 (S 15)

                       or OASIS
or Oberon or Objex

or Ocularis or Odin
or OEone HomeBase
or OIS or Ojuba Linux
or Olà! or OLERT
or OliOS or Olive BSD
or OmegaOS or Omnia XP
or Omoikane GNU/Linux or OnCore
or Onebase Linux or ONIX
or On Time RTOS-32 or Opal
or OpenArtist or Open AT OS
or OpenBeOS or Open BSD
or OpenDarwin or Open Desktop
or Open Enterprise or OpenGEU
or OpenLab or OpenLinux
or OpenLX or Open Mamba
or Openmoko Linux or OpenNA Linux
or Open-ProgeX or OpenRavenscar
or OpenRTOS or OpenServer
or OpenSolaris or OpenStep
or OpenSUSE or Open UNIX

or OpenVME  or OpenVMS 

or Openwall GNU/Linux or OpenWrt 

or OpenZaurus or Operator 

or OPhone or Opus

or Oracle Enterprise Linux or Oralux

or Orange OS or ORVYL
or OS or O/S
or OS BK-11 or OS/C
or osCAN or OSD/XC
or OSE or OSE ck
or OSE Epsilon or OS/8
or OSEK/VDX or OS/1100
or OSE166 or OSE Realtime Kernel
or OS/ES or OSF/1
or OS/4 or OS/400
or OS4000 or OS-IV
or OSm or OS/MFT

or OS/MVS or OS/MVT
or OS-9 or OS-9000

or OS/PCP or OS/RT
or OS7 or OS/700
or OS6 or OSSO

or OS/10 or OS-3

or OS/32-MT or OS/32-ST

or OS/390 or OS/390 OpenEdition

or OS/390 UNIX or OS/360

or OS/2 or OS/200
or OS2000 or OS/2 Warp
or OS/VS1 or OS/VS2
or OSx or Owl
or OZONE or OzOS