| 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 |
| ck1 | CARE-S InfoWorks Kjeldahl Nitrogen Detail 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 |
| cks | PSI-BLAST Checkpoint Sequence Data |
| ckt | Ansys Chemkin Thermodynamic Data |
| ckv | CheckVision Database |
| cky | DSOrganize Data |
| ckz | QuickSFV Checksum Database |
| cl | Carlson Survey Centerline File |
| cl | IconUtils Cursor Library |
| cl | QIP Contact List Data |
| cl2 | Hy-Tek Meet Manager Results Data |
| cl7 | Free Clipboard Viewer Saved Data |
| clam | Adobe InDesign User Dictionary Data |
| classlist | SMART Notebook Class List |
| clb | Corel Mosaic 5.0 Library |
| clb | ICQ Contact List Data |
