Penny's OS 2.0 (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