| xccolortheme | Xcode Color Theme Data |
| xcd | WarpIN Data File |
| xcesession | PDFXEdit Session Data |
| xci | Switch Gamecard Dump Image |
| xclpack | PDFXEdit UI Language Pack |
| xcn | GenePattern XCN Data |
| xco | Xilinx CORE Generator Log |
| xcorpus | Xaira Corpora Data |
| xcos | Scilab Xcos Data |
| xcp | Casio ClassPad 300 Exported ClassPad |
| xcs | TBX eXtensible Constraint Specification |
| xcsl | CineStyle Color Correction Data |
| xcsr | Oracle UCM Content Folio XML |
| xcst | Oracle UCM Content Folio Template |
| xct | ExtremeCopy Task |
| xctl | LabVIEW XControl Data |
| xcvault | XCVault Utility Data |
| xcworkspace | Xcode Workspace Data |
| xd0 | XTreeGold for Dos Help Data |
| xdat | XMVB Data File |
| xdb | Norton Antivirus Update |
| xdb | xFarDic Dictionary Data |
| xdb | Xtext Compiled Database |
| xdd | XFIT XDD Format Data |
| xdelta | Xdelta Binary Differential Data |
| xdf | TunerPro Definition File |
| xdf | Workshare Synergy XDF Data |
| xdl | Expert Definition Language Document |
| xdm | Oracle BI Publisher Data Model |
| xdmz | Oracle BI Publisher Compressed Data Model |
