| ciw | EndNote Web of Science Export |
| cix | IBM Rational XDE Collaboration Instance File |
| cjb | Autodesk Cleaner XL Job |
| ck9 | Cook'n Cookbook Backup |
| cka | Comfort Keys Database |
| ckl | DISA STIG Checklist |
| ckn | Disk Doctors CK Support Info File |
| ckv | CheckVision Database |
| cky | DSOrganize Data |
| ckz | QuickSFV Checksum Database |
| cl | Carlson Survey Centerline File |
| clb | Corel Mosaic 5.0 Library |
| clb | ICQ Contact List Data |
| clb | NoteTab Clipbook Library |
| clbu | Android Call Log Backup |
| clbx | MP3 Automagic CD Cover Creator Label |
| clc | Corel Mosaic 5.0 Catalogue |
| cld | ClamAV Local Database |
| clean | Instagram for Android Cache Data |
| clf | ListPro Data |
| clf1 | Common Loudspeaker Format Type 1 File |
| clf2 | Common Loudspeaker Format Type 2 File |
| clh | NoteTab Clip Assistant List |
| clib | CATS Library File |
| clkc | Clicker Connect Set |
| clkk | Clicker Keyboard |
| clkp | Clicker Palette |
| cll | Crick Software Clicker Data |
| clm | GenePattern CEL Descriptor |
| cloc | CATS Location File |
| cloud | GOM Atos Point Cloud Data |
| clp | MakeMusic Finale Clip File |
| clpi | Blu-ray Disc Clip Information |
| clr | FARSITE Color Data |
| clr | MODTRAN Cooling Rate Data |
