| 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 |
| clsid | CLSID Identifier Data |
| clsj | CyberLink PowerDVD 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 |
| cm | NucleoView Image Data |
| 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 |
| cm8 | CaseMap 8 Data |
| cma | Coach Activity File |
| cmac | CICS CMAC Messages Data Set |
| cmap | CmapTools Concept Map |
| cmautosave | CET Designer Drawing Autosave |
| cmax | CMax Circuit Data |
| cmb | Reason Combinator Instrument Patch |