| 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 | Cytoscape Session File |
| cys | Clustify Summary File |
| cyt | Crocodile Technology Simulation Data |
| cz | Czech Language Related Text |
| czn | RMCProfile Carbon Zinc Neighbours Data |
| czp | ClozePro Archive |
| czr | Everest Advanced Report |
| d01 | MicroSim PCBoard Drill Data |
| d05 | MicroSim PCBoard Drill Data |
| d07 | DeductionPro 2007 Data |
| d08 | MicroSim PCBoard Drill Data |
| d1 | Progress OpenEdge Database |
| d10 | IRIG 106 Recording Directory Data |
| d2 | Progress OpenEdge Database |
| d2e | Gaussian Two-Electron Integral Derivative File |
| d2f | Dvd2Avi D2F Data |
| d3d | Game Maker 3D Data |
| d3p | DigitalPrintLab 3 Data |
| d3plot | Oasys D3PLOT Data |
| d4 | Titan Showfile |
| d4b | Titan Showfile Backup |
| d7d | Dewesoft 7 Data |
| d7s | Dewesoft 7 Setup Data |
| d7t | Dewesoft 7 Sequence Data |
| d83 | GAEB 1990 Data File |
