| Extension | File Description |
| .UKA | Uncommon Files |
| .UKB | Uncommon Files |
| .UKC | Uncommon Files |
| .UKD | Uncommon Files |
| .UKE | Uncommon Files |
| .UKF | Uncommon Files |
| .UKG | Uncommon Files |
| .UKH | Uncommon Files |
| .UKI | Uncommon Files |
| .UKJ | Uncommon Files |
| .UKK | Uncommon Files |
| .UKL | Uncommon Files |
| .UKM | Uncommon Files |
| .UKN | Uncommon Files |
| .UKO | Uncommon Files |
| .UKP | Uncommon Files |
| .UKQ | Uncommon Files |
| .UKR | Uncommon Files |
| .UKS | Uncommon Files |
| .UKT | Uncommon Files |
| .UKU | Uncommon Files |
| .UKV | Uncommon Files |
| .UKW | Uncommon Files |
| .UKX | Game Files |
| .UKY | Uncommon Files |
| .UKZ | Uncommon Files |
| .UK_ | Uncommon Files |
| .UL | Uncommon Files |
| .UL0 | Uncommon Files |
| .UL1 | Uncommon Files |
| .UL2 | Uncommon Files |
| .UL3 | Uncommon Files |
| .UL4 | Uncommon Files |
| .UL5 | Uncommon Files |
| .UL6 | Uncommon Files |
| .UL7 | Uncommon Files |
| .UL8 | Uncommon Files |
| .UL9 | Uncommon Files |
| .ULA | Uncommon Files |
| .ULB | Uncommon Files |
| .ULC | Uncommon Files |
| .ULD | Uncommon Files |
| .ULE | Uncommon Files |
| .ULF | Data Files |
| .ULG | Uncommon Files |
| .ULH | Uncommon Files |
| .ULI | Uncommon Files |
| .ULJ | Uncommon Files |
| .ULK | Uncommon Files |
| .ULL | Uncommon Files |
| .ULM | Uncommon Files |
| .ULN | Uncommon Files |
| .ULO | Uncommon Files |
| .ULP | Uncommon Files |
| .ULQ | Uncommon Files |
| .ULR | Uncommon Files |
| .ULS | Misc Files |
| .ULT | Audio Files |
| .ULU | Uncommon Files |
| .ULV | Uncommon Files |
| .ULW | Audio Files |
| .ULX | Uncommon Files |
| .ULY | Uncommon Files |
| .ULZ | Data Files |
| .UM | Uncommon Files |
| .UM0 | Uncommon Files |
| .UM1 | Uncommon Files |
| .UM2 | Uncommon Files |
| .UM3 | Uncommon Files |
| .UM4 | Uncommon Files |
| .UM5 | Uncommon Files |
| .UM6 | Uncommon Files |
| .UM7 | Uncommon Files |
| .UM8 | Uncommon Files |
| .UM9 | Uncommon Files |
| Extension | File Description |
| .UMA | Uncommon Files |
| .UMB | Uncommon Files |
| .UMC | Uncommon Files |
| .UMD | Uncommon Files |
| .UME | Uncommon Files |
| .UMF | Uncommon Files |
| .UMG | Uncommon Files |
| .UMH | Uncommon Files |
| .UMI | Uncommon Files |
| .UMJ | Data Files |
| .UMK | Uncommon Files |
| .UML | Developer Files |
| .UMM | Uncommon Files |
| .UMN | Uncommon Files |
| .UMO | Uncommon Files |
| .UMOD | Game Files |
| .UMP | Uncommon Files |
| .UMQ | Uncommon Files |
| .UMR | Uncommon Files |
| .UMS | 3D Image Files |
| .UMT | Uncommon Files |
| .UMU | Uncommon Files |
| .UMV | Uncommon Files |
| .UMW | Uncommon Files |
| .UMX | Game Files |
| .UMY | Uncommon Files |
| .UMZ | Uncommon Files |
| .UN0 | Uncommon Files |
| .UN1 | Uncommon Files |
| .UN2 | Uncommon Files |
| .UN3 | Uncommon Files |
| .UN4 | Uncommon Files |
| .UN5 | Uncommon Files |
| .UN6 | Uncommon Files |
| .UN7 | Uncommon Files |
| .UN8 | Uncommon Files |
| .UN9 | Uncommon Files |
| .UNA | Uncommon Files |
| .UNASSIGNED | Uncommon Files |
| .UNB | Uncommon Files |
| .UNC | Uncommon Files |
| .UNCIAL | Uncommon Files |
| .UND | Uncommon Files |
| .UNE | Uncommon Files |
| .UNF | Uncommon Files |
| .UNG | Uncommon Files |
| .UNH | Uncommon Files |
| .UNI | Audio Files |
| .UNIKEY | Uncommon Files |
| .UNION | Uncommon Files |
| .UNITYWEB | Data Files |
| .UNIVERSAL3 | Uncommon Files |
| .UNIX | Uncommon Files |
| .UNJ | Uncommon Files |
| .UNK | Uncommon Files |
| .UNKNOWN | Misc Files |
| .UNL | Misc Files |
| .UNLOCK | Uncommon Files |
| .UNM | Uncommon Files |
| .UNN | Uncommon Files |
| .UNO | Uncommon Files |
| .UNP | Uncommon Files |
| .UNPAC | Uncommon Files |
| .UNPACK | Uncommon Files |
| .UNQ | Uncommon Files |
| .UNR | Game Files |
| .UNS | Uncommon Files |
| .UNT | CAD Files |
| .UNU | Uncommon Files |
| .UNUSED | Uncommon Files |
| .UNV | Uncommon Files |
| .UNW | Uncommon Files |
| .UNX | Text Files |
| .UNY | Uncommon Files |
| .UNZ | Uncommon Files |
