| UREP | UNIX-RSCS Emulation Program [BITNET software for UNIX] |
| UUCP | UNIX to UNIX Copy Program / Protokoll |
| UUCP | Unix-to-Unix CoPy |
| U | Unix |
| LM/X | LAN Manager for Unix |
| XINU | Xinu Is Not UNIX |
| UI | Unix International |
| SFU | Services For Unix |
| DBX | Debugger for UNIX |
| EUnet | European UNIX Network |
| AUX | Apple UNIX [engl.] |
| UAB | UNIX Appletalk Bridge |
| UUG | Unix User Group |
| OLIX | On-Line Informationssystem UNIX |
| SVR4 | UNIX System V Release 4 |
| PUPS | PDP UNIX Preservation Society |
| RTU | Real Time Unix |
| UMM | Unix Macro Magician |
| USO | UNIX Software Operation |
| TUHS | The UNIX Heritage Society |
| SVID | Unix System V Interface Definition |
| SVVS | UNIX System V Validation Suite |
| UCFS | Unix Connectivity File Service |
| UFS | Universal / UNIX File System |
| UID | Unique / Unix / User Identifier |
| UIAP | UNIX International Asia / Pacific |
| USL | UNIX System Laboratories [AT&T, Novell] |
| USLE | UNIX System Laboratories Europe |
| SUUG | Soviet UNIX User Group |
| SI | Simple Interface [Cray to UNIX] |
| CUPS | Common UNIX Printing System |
| DKUUG | Danish UNIX Users' Group |
| EUC | Enhanced/Extended UNIX Code |
| EUROPEN | Dachverband europäischer UNIX-Anwendervereinigungen |
| EUUG | European UNIX Users Group |
| GNU | GNU's Not Unix [rekursives Akronym] Boston, http://www.gnu.org |
| GUMM | Gurus of UNIX Meeting of Minds |
| GUN | Gemeinschaft der UNIX-Anwender Niederrhein |
| GUUG | German Unix User Group Köln, http://www.guug.de |
| JUNET | Japan/Japanese UNIX Network |
| SAGE | System Administrators' Guild [UNIX] |
| NLUUG | Niederländische UNIX User Group |
| MOSIX | Multicomputer Operating System for UNIX |
| LUUG | Lunar UNIX Users Group |
| LPD | Line Printer Daemon [UNIX] |
| KUUG | Karlsruher UNIX User Group |
| USG | UNIX Support / System Group [Novell] |
| UNICOS | UNIX-based Cray Operating System |
| BUUG | Belgian UNIX-User Group [engl.] |
| UUU | Unknown UNIX User [J. Random Hacker?] |