| cxl | Tekla Structural Designer Neutral Data |
| cxm | QuadColor Color Correction Master Data |
| cxml | Silverlight PivotViewer XML Data |
| cxo | CXInsight Export Data |
| cxp | Crocodile Physics Simulation Data |
| cxr | FMAT Plate Results Data |
| cxs | ConciseXML Format Data |
| cxt | Crocodile Technology Simulation Data |
| cxv | Custody X Change Data |
| cy3 | Cytel StatXact 5.0 Data |
| cyb | Cytel Studio Batch |
| cyd | LogXact Data |
| cyd | Cytel Studio Data |
| cyg | CyGem Pollux Data |
| cyl | Cytel LogXact Data |
| cyl | Ribbons Cylinder Definition |
| 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 |
| d01 | MicroSim PCBoard Drill Data |
| d07 | DeductionPro 2007 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 |