| ctr | BrainVoyager QX Contrast Data |
| cts | GodswMobile Contacts Transfer Backup |
| cts | CrazyTalk Script |
| ctt | ETCBC Coded Text Tabulated Data |
| ctt | MSN Messenger Contact List |
| ctx | CyberTracker Exported Data |
| ctz | Cherrytree Password Protected Data |
| cu | CU-SeeMe Data |
| cu | my Knowledge Explorer Change Unit |
| cu1 | PhotoLine 4 Curve Data |
| cu3 | PhotoLine 4 Curve Data |
| cub | Gaussian Cube Data |
| cub | ISIS 2 Cube |
| cube | Gaussian Cube Data |
| cuce | CU-SeeMe Data |
| cud | ChmUpDate Data |
| cudt | ClarisWorks User Dictionary Data |
| cuix | Autodesk AutoCAD Custom User Interface |
| cul | Windows Cursor Library |
| cup | Naviter SeeYou Waypoint Data |
| cur | Oasys T/HIS Curve File |
| cursorfx | CursorFX Theme |
| curv | Genetica Mathematical Curve |
| curve | ANSYS TurboGrid Curve File |
| curxptheme | CursorXP Theme |
| cus | Autodesk AutoCAD Custom Dictionary |
| cus | WindLDR Custom Monitor Data |
| cut | GMFC Foam Cutting Data |
| cuts | TS-Doctor Cuts Data |
| cuv | Origin Sample Curve Data |
