| .USTAR | Smith Micro Software | Datafiler | Uniform Standard Tape Archive Format File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .UU | Open Source | Krypterte filer | Uuencoded File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .UUE | Open Source | Krypterte filer | Uuencoded File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .WAR | Oracle Corporation | Komprimerte filer | Java Web Archive | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .WMZ | Microsoft Corporation | Innstillingsfiler | Compressed Windows Media Player Skin | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .Y | Microsoft Corporation | Rasterbildefiler | Subsampled Raw YUV Image | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .YENC | Open Source | Krypterte filer | yEnc File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .YNC | Open Source | Krypterte filer | yEnc Encoded File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .Z | Smith Micro Software | Komprimerte filer | Unix Compressed File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .Z01 | Corel | Komprimerte filer | WinZip First Split Zip File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .Z02 | Corel | Komprimerte filer | WinZip Second Split Zip File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .Z03 | Corel | Komprimerte filer | WinZip Third Split Zip File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .Z04 | Corel | Komprimerte filer | WinZip Fourth Split Zip File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .Z05 | Corel | Komprimerte filer | WinZip Fifth Split Zip File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .Z06 | Corel | Komprimerte filer | WinZip Sixth Split Zip File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .Z07 | Eugene Roshal | Komprimerte filer | Split Multi-volume RAR Compressed File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .Z08 | Eugene Roshal | Komprimerte filer | Split Multi-volume RAR Compressed File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .Z09 | Eugene Roshal | Komprimerte filer | Split Multi-volume RAR Compressed File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .Z96 | Eugene Roshal | Komprimerte filer | Split Multi-volume RAR Compressed File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .ZIP | Winrar | Komprimerte filer | Zipped File | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .ZIP2 | Smith Micro Software | Komprimerte filer | StuffIt Archive | Smith Micro StuffIt Deluxe | Smith Micro Software |
| .ZPI | Winrar | Komprimerte filer | Zipped File | Smith Micro StuffIt Deluxe | Smith Micro Software |
av 2 
