| ufed | CelleBrite UFED Data |
| uff | BrainVoyager QX User Defined File Format |
| uff | Scream Universal File Format Data |
| ufi | User Flash Image |
| ufl | Verity Server Custom Fields File |
| ufo | PhotoImpact Object |
| ufo | SNES ROM Image UFO |
| ufraw | Unidentified Flying Raw Data |
| uft | Torque Font Cache |
| ufx | Ultimate 3D Effects Data |
| ugf | Go Game Data |
| ugi | Go Game Data |
| ugp | Aroma Unit Genome Position Data |
| ugr | Apophysis Gradient File |
| ugrid | Delft3D Flexible Mesh Suite UGRID Data |
| ugz | Compressed Go Game Data |
| uhh | Eurotherm 6100a Binary Data |
| uhh | Eurotherm Hydra History Data |
| uhi | Eurotherm 6100a Printer Driver Import Data |
| uhq | Eurotherm 6100a Support Data |
| uhr | Eurotherm 6100a User Resource Data |
| uhs | Universal Hint System Hints File |
| uht | Eurotherm 6100a Table Data |
| uhu | Eurotherm 6100a User Screen Data |
| ui | Gimp Plug-ins UI Data |
| uid | IBM VoiceType User Data |
| uid-zps | Zoner Photo Studio Changes Backup Data |
| uil | AIX User Interface Language |
| uin | ICQ 2001 Saved ICQ Contacts Information |
| uis | Stardock WindowsBlinds Style Description |
