| cli | AquaCrop Climate Data |
| clib | CATS Library File |
| clipping | Mac Text Clipping Data |
| clkc | Clicker Connect Set |
| clkk | Clicker Keyboard |
| clkm | Clicker Matching Set |
| clkp | Clicker Palette |
| clks | Clicker Sentences Data |
| clktk | Clicker Talk Set |
| clkv | Clicker Communicator Vocabulary Set |
| cll | Crick Software Clicker Data |
| clm | Clipboard Master Data |
| clm | GenePattern CEL Descriptor |
| clm2 | Clipboard Master Data |
| clm4 | Clipboard Master Data |
| clmlic | Clipboard Master License Data |
| clo | SPSS Chalkboard Data |
| cloc | CATS Location File |
| clonecd | CloneCD Registration Data |
| clonedvd | CloneDVD Registration Data |
| 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 |
| clr0 | Nintendo Wii Color Swapping Animation 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 |
