Penny's OS (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