| Nitix | — | — | — |
| Nitrux | Camilo Higuita | — | — |
| NixOS | Thomas Tuegel, Eelco Dolstra | — | MIT License |
| NLTSS | Lawrence Livermore National Laboratory | — | — |
| NND | — | — | — |
| Nobara (operating system) | Thomas Crider | — | — |
| NodeOS | — | — | MIT License |
| NOI Linux | — | — | — |
| Nokia Asha platform | Nokia, Microsoft Mobile | — | — |
| Nokia Fastlane | Nokia | — | — |
| Nokia X | — | — | — |
| NomadBSD | — | 2018 | 2-clause BSD License |
| NonStop OS | Tandem Computers | — | — |
| Nonux | — | — | GNU General Public License |
| NORD | — | — | — |
| NorthStar DOS | North Star Computers | — | — |
| NORTON-BK | — | — | — |
| NOS | Alien Internet Services | — | — |
| NOS | Control Data Corporation | — | — |
| NOS/VE | Control Data Corporation | — | — |
| Not Another Completely Heuristic Operating System | — | — | BSD licenses |
| Nothing OS | Nothing Technology Ltd. | — | Android Open Source Project |
| Nova | University of Information Science | 2014 | GNU General Public License |
| Novell S-Net | Novell | — | — |
| NUbuntu | — | — | — |
| Nucleus RTOS | Mentor Graphics | — | — |
| Nura | — | — | GNU General Public License, version 3.0 |
| Nut/OS | Ethernut | 2000 | BSD licenses |
| NuttX | Apache Software Foundation | — | Apache License, Apache Software License 2.0 |
| NuTyX | — | — | GNU General Public License |
| NVIDIA DGX OS | Nvidia | — | — |
| NX-OS | Cisco | — | — |
| Nyarch | — | — | — |
| OASIS operating system | — | — | — |
| Oberon | Niklaus Wirth | — | BSD licenses |
| OcNOS | IP Infusion | — | proprietary license |
| Octopus | — | — | — |
| OctOS | — | — | — |
| Odebian | — | — | — |
| Ojuba Linux | — | — | GNU General Public License |
| Olivetti X/OS | Olivetti | — | — |
| Omarchy | David Heinemeier Hansson | — | MIT License |
| OmniROM | — | 2013 | Apache License |
| One UI Core | — | — | — |
| Online OS | — | — | European Union Public Licence |
| ONTAP | NetApp | — | — |
| Open Enterprise Server | Novell | — | — |
| Open School Server | — | — | — |