| TvOS 15 | Apple Inc. | — | — |
| TvOS 16 | Apple Inc. | — | — |
| TvOS 17 | Apple Inc. | — | — |
| TvOS 9 | Apple Inc. | — | Apple Public Source License |
| Twister OS | — | — | freeware |
| Ubuntu 24.04 | Canonical Ltd. | 2024 | — |
| Ubuntu for Android | Canonical Ltd. | — | GNU General Public License |
| Ubuntu GNOME | Canonical Ltd. | 2016 | GNU General Public License |
| UCSD p-System | — | — | — |
| UDOS | VEB Robotron | — | — |
| Uenux | — | — | — |
| Ufficio Zero | — | 2020 | GNU General Public License |
| Uhuru Mobile | — | — | — |
| Ultrix | Digital Equipment Corporation | — | — |
| UNICOS | Cray | — | — |
| Unics | — | — | — |
| UniFLEX | Technical Systems Consultants | — | — |
| Unity Linux | — | — | — |
| UNIVAC EXEC I | UNIVAC | — | — |
| UNIVAC EXEC II | Computer Sciences Corporation | — | — |
| Universal Time-Sharing System | Scientific Data Systems | — | — |
| University of Michigan Executive System | University of Michigan | — | — |
| UNIX System III | AT&T Corporation | — | — |
| UNIX System Services | IBM | — | — |
| UNIX System V | AT&T | 1983 | — |
| UNIX/32V | Bell Labs | — | 4-clause BSD License |
| Unix/NS | NCR Corporation | — | — |
| Unslung | — | — | — |
| Unununium | — | — | BSD licenses |
| USIX | — | — | — |
| UTS | Amdahl Corporation, UTS Global | 1981 | — |
| UwUntu | — | — | Creative Commons Attribution 4.0 International |
| UXP/DS | Fujitsu | — | — |
| V operating system | David Cheriton | — | — |
| VAXELN | Digital Equipment Corporation | — | — |
| Venix | IntervalZero | 1983 | — |
| Versados | Motorola | — | — |
| Versatile Real-Time Executive | Jim Ready | — | — |
| Version 10 Unix | — | — | — |
| Version 6 Unix | Bell Labs | 1975 | 4-clause BSD License, proprietary license |
| Version 7 Unix | — | — | 4-clause BSD License |
| Version 8 Unix | — | — | — |
| Version 9 Unix | — | — | — |
| Verve | Microsoft Research | — | — |
| VibeOS | — | 2025 | MIT License |
| Vibrante | Nvidia | — | — |
| VIDAA | Hisense | — | — |
| Viperr | — | — | — |