| clc | Corel Mosaic 5.0 Catalogue |
| clct | RootCause Collect Data |
| cld | ClamAV Local Database |
| cldlyr | Terragen Cloud Layer Data |
| 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 | MODTRAN Cooling Rate Data |
| clr | FARSITE Color Data |
| clsid | CLSID Identifier Data |
| clst | PLINK Cluster Membership File |
| clt | MetaVR 3D Cultural Features Data |
| clu | CLUCalc Script |
| clu | NeuroScope Cluster Data |
| clut | Adobe Photoshop Color Table |
| clx | Ceelox SecureMail Secure Message |
| cly | Act! Design Layout File |
| cm0013 | Samsung Smart TV Device Information |
| cm10 | CaseMap 10 Data |
| cm2 | Poser Camera Data |
| cm3 | CaseMap 3 Data |
| cm4 | CaseMap 4 Data |
| cm5 | Clone Manager Molecule Data |