| cik | CorelDRAW Graphics Custom Dual Tone Settings Data |
| cikernel | CIKernel Data |
| cilx | VAMT Computer Information List |
| cim | Cimplicity HMI Screen |
| cin | Microsoft Cinemania Data |
| cin96lm | Microsoft Cinemania Data |
| cin96upd | Microsoft Cinemania Data |
| cio | SWAT Master Watershed Data |
| cip | Ghost Keylogger Logfile |
| cir | Altair FEKO SPICE Circuit Data |
| cir | Cadence PSpice Circuit Data |
| cir | Ngspice Circuit Data |
| cir | Racelogic PerformanceBox Circuit Overlay |
| circ | Logisim Circuit Data |
| cis2 | CIMSteel Integration Standard 2 Document |
| citygml | CityGML Data |
| ciw | EndNote Web of Science Export |
| cix | IBM Rational XDE Collaboration Instance File |
| cjb | Autodesk Cleaner XL Job |
| cjd | Casio EX-word Dictionary Data |
| cjk | Latex CJK Package Data |
| cjstyles | Skin Framework Style Data |
| ck9 | Cook'n Cookbook Backup |
| cka | Comfort Keys Database |
| cki | Ansys Chemkin Kinetic Data |
| cki | Off by One Web Browser Cookie Data |
| ckl | DISA STIG Checklist |
| ckn | Disk Doctors CK Support Info File |
| ckp | Ingres Database Checkpoint Data |
| ckp | PSI-BLAST Checkpoint Profile Data |
