| Pocket PC 2002 | Microsoft | — | — |
| PocketPC 2000 | Microsoft | 2000 | — |
| Polippix | — | — | — |
| Pop!_OS | System76 | 2017 | GNU General Public License |
| Porteus | — | — | GNU General Public License |
| Poseidon Linux | — | — | — |
| PowerLinux | IBM | — | — |
| PowerNex | — | — | Mozilla Public License, version 2.0 |
| Predator OS | — | — | — |
| Prex | — | — | BSD licenses |
| PRIMOS | Prime Computer | — | — |
| PrimTux | — | — | GNU General Public License, version 3.0 |
| PrivatOS | Silent Circle | 2014 | — |
| Progeny Componentized Linux | Progeny Linux Systems | — | — |
| ProteanOS | — | — | — |
| Proxmox Backup Server | — | — | GNU Affero General Public License, version 3.0 |
| Proxmox Mail Gateway | — | — | — |
| Proxmox Virtual Environment | Proxmox Server Solutions GmbH | — | GNU Affero General Public License, version 3.0 |
| PTS-DOS | Paragon Software Group | 1993 | proprietary license |
| Puavo | — | — | GNU General Public License, version 2.0 |
| Publik | — | — | GNU General Public License, Affero General Public License |
| PUD | — | — | — |
| Puppy Linux | — | 2003 | GNU General Public License |
| PureDarwin | — | — | — |
| Puredyne | — | — | — |
| PureNexusProject | — | 2012 | — |
| PureOS | Purism | — | Creative Commons Attribution-ShareAlike 4.0 International |
| PWB/UNIX | Bell Labs | 1977 | — |
| PX5 RTOS | William Lamie | — | — |
| Pyabr | — | — | — |
| Q4OS | — | 2013 | GNU General Public License |
| Qasedak distro | — | — | — |
| QiLinux | — | — | GNU General Public License |
| Qimo | — | — | — |
| Qimo 4 Kids | — | — | GNU General Public License |
| QNodeOS | QuTech | — | — |
| QNX | BlackBerry, QNX Software Systems | — | — |
| QP | — | — | GNU General Public License |
| Qt Extended | Qt Group Plc | — | GNU General Public License |
| QtMoko | — | — | — |
| Quantian | Dirk Eddelbuettel | — | GNU General Public License |
| Qubes OS | — | — | GNU General Public License, version 2.0 |
| R9 | — | — | MIT License |
| RadiOS | — | — | — |
| Rainbow-OS | Ulm University | — | — |
| RAMON | — | — | — |
| RancherOS | Rancher Labs | — | Apache Software License 2.0 |
| Raspberry Pi OS | Raspberry Pi Holdings | 2012 | GNU General Public License |