| Trustix | Comodo Group | — | GNU General Public License |
| TSS-8 | Digital Equipment Corporation | 1968 | proprietary license |
| TSS/360 | IBM | 1967 | — |
| TSX-32 | — | — | — |
| TSX-Plus | — | — | — |
| TTOS Linux | — | — | — |
| Tucunaré | — | — | — |
| Tuga | — | — | GNU General Public License |
| Tukaani Linux | — | — | — |
| Turbo Rom | — | — | — |
| TurboDOS | — | — | — |
| Turkix | — | — | — |
| TurnKey Linux Virtual Appliance Library | — | — | — |
| Turtlebot | — | — | BSD licenses |
| Tuxedo OS | — | — | — |
| TvOS | Apple Inc. | — | Apple Public Source License |
| TvOS 10 | Apple Inc. | — | Apple Public Source License |
| TvOS 11 | — | — | — |
| TvOS 12 | — | — | — |
| TvOS 13 | Apple Inc. | 2019 | Apple Public Source License |
| TvOS 14 | Apple Inc. | 2020 | Apple Public Source License |
| TvOS 15 | Apple Inc. | — | — |
| TvOS 16 | Apple Inc. | — | — |
| TvOS 17 | Apple Inc. | — | — |
| TvOS 26 | Apple Inc. | — | — |
| TvOS 9 | Apple Inc. | — | Apple Public Source License |
| Twister OS | — | — | freeware |
| TWRP | — | — | GNU General Public License |
| U-Lite | — | — | GNU General Public License |
| UberStudent | — | — | GNU General Public License |
| Ubix Linux | — | — | — |
| Ubuntu | Canonical Ltd. | 2004 | — |
| Ubuntu 24.04 | Canonical Ltd. | 2024 | — |
| Ubuntu Budgie | — | — | GNU General Public License |
| Ubuntu Christian Edition | User community | — | — |
| Ubuntu Cinnamon | — | — | — |
| Ubuntu Core | — | — | — |
| Ubuntu for Android | Canonical Ltd. | — | GNU General Public License |
| Ubuntu GNOME | Canonical Ltd. | 2016 | GNU General Public License |
| Ubuntu Kylin | National University of Defense Technology | — | GNU General Public License |
| Ubuntu MATE | — | — | GNU General Public License |
| Ubuntu Mobile | Canonical Ltd. | — | GNU General Public License |
| Ubuntu Netbook Edition | Canonical Ltd. | — | GNU General Public License |
| Ubuntu Privacy Remix | — | — | — |
| Ubuntu Satanic Edition | — | — | — |
| Ubuntu Server Edition | Canonical Ltd. | 2006 | GNU General Public License |
| Ubuntu Studio | Canonical Ltd., Ubuntu Foundation | 2007 | GNU General Public License |
| Ubuntu Sway Remix | — | — | — |