| Raspberry Pi OS | Raspberry Pi Holdings | 2012 | GNU General Public License |
| Redox | Jeremy Soller | — | MIT License |
| RTEMS | Sebastian Huber, Joel Sherrill | — | GNU General Public License |
| SkyOS | Robert Szeleney | 1997 | — |
| Sortix | Jonas Termansen | 2011 | ISC license |
| Soso | — | — | 2-clause BSD License |
| SPIX | Groupe Bull | — | proprietary license |
| Syllable Desktop | — | — | GNU General Public License |
| Tropix | Federal University of Rio de Janeiro | — | — |
| Tru64 UNIX | Hewlett-Packard, Digital Equipment Corporation, IBM, Compaq | — | proprietary license |
| Ubuntu | Canonical Ltd. | 2004 | — |
| UnixWare | Novell, SCO Group, Caldera, Santa Cruz Operation, Univel | — | proprietary license |
| UX/RT | — | — | — |
| VisionOS | Apple Inc. | — | — |
| VMware ESXi | VMware | — | — |
| VSTa | — | — | GNU General Public License |
| WatchOS | Apple Inc. | — | — |
| WEGA | EAW | — | — |
| Xenix | Microsoft, Santa Cruz Operation, AT&T Corporation | — | proprietary license |
| Xinuos OpenServer | Santa Cruz Operation, Xinuos | — | proprietary license |
| Z/OS | IBM | 2001 | — |