| ckt | B2-Spice Circuit Design |
| Crocodile Clips Data |
| ckv | CheckVision Database |
| cky | DSOrganize Data |
| ckz | QuickSFV Checksum Database |
| cl | Carlson Survey Centerline File |
| IconUtils Cursor Library |
| 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 |
| ICQ Contact List Data |
| NoteTab Clipbook Library |
| clbu | Android Call Log Backup |
| clbx | MP3 Automagic CD Cover Creator Label |
| clc | Corel Mosaic 5.0 Catalogue |
| Schedule Plus Habits Mission Statement Data |
| UltimaCalc Data |
| clct | RootCause Collect Data |
| cld | ClamAV Local Database |
| Terragen Cloud Layer Data |
| cldcvt | CD-LabelPrint Converted Data |
| cldlyr | Terragen Cloud Layer Data |
| cle | Icon Lock-iT XP Locked File Indicator |
| clean | Instagram for Android Cache Data |
| clf | DesignWorks Library |
| ListPro Data |
| Source Insight Custom Language Data |
| clf1 | Common Loudspeaker Format Type 1 File |
| clf2 | Common Loudspeaker Format Type 2 File |
| clg | Microsoft Windows Catalog Data |
| QIP Ignored Contact List Data |
| clh | NoteTab Clip Assistant List |
| cli | AquaCrop Climate Data |
| clib | CATS Library File |
| client | Telepathy Interface Client Data |
| clipping | Mac Text Clipping Data |
| clk | ClickFORMS 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 |
| GenePattern CEL Descriptor |
| MagicJack Call Log |
| Micrografx Picture Publisher Macro |
| clm2 | Clipboard Master Data |
| clm4 | Clipboard Master Data |
| clmlic | Clipboard Master License Data |
| clo | SPSS Chalkboard Data |
| cloc | CATS Location File |
| clog | SpreadMaster Client Log |
| clonecd | CloneCD Registration Data |
| clonedvd | CloneDVD Registration Data |
| cloud | GOM Atos Point Cloud Data |
| clp | CA-Clipper Compiler Script |
| Corel Quattro Pro Clipart |
| CrazyTalk Clip Data |
| MakeMusic Finale Clip File |
| Windows Clipboard File |
| clpi | Blu-ray Disc Clip Information |
| clr | Adobe Flash Color Table |
| Aldus PhotoStyler Color Definitions Data |
| Apple Color Picker Palette |
| CryptLoad Router Information |
| FARSITE Color Data |
| FileMaker Pro Spelling Dictionary |
| MODTRAN Cooling Rate Data |
| Vue Color Map Data |
| WinMX Color Scheme |
| clr0 | Nintendo Wii Color Swapping Animation Data |
| cls | AOL Instant Messenger Class Data |
| LaTeX Document Class Data |
| clsid | CLSID Identifier Data |
