Penny's OS (S 3)

   
                                    or Cache kernel
or Caixa Mágica or Calculate Linux
or Caldera OpenLinux or Calmira
or Cambridge CAP or Cambridge Ring
or CAOS Linux or Capital OS
or CapROS or CAPS-8
or CAPS-11 or CarLOS
or Càtix or CatOS
or CB Unix or CCP
or CCux Linux or CD Linux
or CDOS or Cefarix
or Censornet or CentOS
or C Executive or Chakra
or Chaos or Charlotte
or ChibiOS/RT or Chimera
or Chios or CHIPPEWA
or CHOICES or Chorus
or Chrome OS or Chromium OS
or CiMOS or Cinder OS
or Cisco IOS or ClarkConnect
or ClearOS or Cleese
or Clicker 32 or Clix
or ClosedBSD or Clouds
or Clusterix or ClusterKnoppix
or CMAS or CMDS
or CMS or CMX RTX
or CobaltOS or COBRA
or COCANET UNIX or Co-Create
or Coherent or Collax
or Concurrent CP/M-86 or Concurrent DOS
or CONDOR or Condorux
or Conectiva Linux or Consensys
or Contiki or Convergent Technologies
or ConvexOS or Coollinux
or Cooperative Linux or COPSY
or Coreboot or Corel Linux
or COS or Cosmoe
or Cosmos or cos2000
or COSY or Counterpoise
or Coyote Linux or Coyotos
or CP or CP/CMS
or CPF or CP-40
or CP/K or CP/M
or CP/M-86 or CP/M Plus
or CP/NET or CPPS
or CPS or CP-6
or CP-67 or CP-370
or CP/Z or Craftworks Linux
or Cray OS or CROMIX
or Cronus or Croquet
or CrunchBang Linux or CrunchEee
or CRUX or Crypto
or CSI-DOS or CTIX
or CTOS or CTRON
or CTSS or CTS-300
or CXOs or CX/UX
or Cyber or Cygnus
or CyROS or Cy/VOS