| 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 |
| 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 |
| 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 |
| cmax | CMax Circuit Data |
| cmb | Reason Combinator Instrument Patch |
| cmb | SGI Scalable Graphics Compositor Combination File |
| cmbd | GMI WellCheck Combined File |
| cmbl | Vernier Logger Pro Data |
| cmc | Comic Collector Collection Data |
| cmd5 | CrystalMaker V5 Data File |
| cmdb | CFX Mesh Database |
| cmdf | CrystalMaker V2 Data File |
| cmdl | Cafu Engine Model Data |