| cxs | ConciseXML Format Data |
| cxt | Crocodile Technology Simulation Data |
| cxt | CX-Programmer Text Data |
| cxv | Custody X Change Data |
| cy | Cyberware 3D Scanner Data |
| cy3 | Cytel StatXact 5.0 Data |
| cya | Adobe Photoshop Cyan Color Separation Data |
| cyb | Cytel Studio Batch |
| cyberducklicense | Cyberduck License Data |
| cyd | Cytel Studio Data |
| cyd | LogXact Data |
| cydb | Alteryx Designer Calgary Database |
| cyg | CyGem Pollux Data |
| cyh | CyberHttp Injector Data |
| cyidx | Alteryx Designer Calgary Database Index |
| cyl | Cytel LogXact Data |
| cyl | Ribbons Cylinder Definition |
| cylc | Alteryx Designer Calgary License Data |
| cym | AdPlug Callus YM2151 Register Log |
| cyo | Clustify Output |
| cyp | Crocodile Physics Simulation Data |
| cys | Clustify Summary File |
| cys | Cytoscape Session File |
| cyt | Crocodile Technology Simulation Data |
| czn | RMCProfile Carbon Zinc Neighbours Data |
| czp | ClozePro Archive |
| czr | Everest Advanced Report |
| czs | WinEcran Screen Link |
| d | ChemDraw Chemical Modeller Output |
| d$$ | AGT Game Encrypted Message |
| d01 | MicroSim PCBoard NC Drill Data |
| d02 | MicroSim PCBoard NC Drill Data |
| d03 | MicroSim PCBoard NC Drill Data |
| d04 | MicroSim PCBoard NC Drill Data |
| d05 | MicroSim PCBoard NC Drill Data |
