| DigitaOS | — | 1998 | — |
| DioneOS | — | — | — |
| DIP-DOS | — | — | — |
| Dirty Unicorns | — | 2012 | GNU General Public License, version 2.0, GNU General Public License, version 3.0 |
| DiskStation Manager | Synology Inc. | — | — |
| Distro Astro | — | — | — |
| DivestOS | — | — | — |
| DNALinux | — | — | — |
| DNIX | Dataindustrier AB | — | — |
| Dolphin OS | — | — | — |
| Domain/OS | Apollo Computer | 1981 | — |
| DOS Plus | Digital Research | — | — |
| DOS/360 | IBM | 1966 | — |
| DOSB10 | — | — | — |
| DotOS | — | 2017 | — |
| DoudouLinux | — | — | — |
| Dpup | — | — | — |
| DR-DOS | DRDOS Inc, Digital Research | — | — |
| Draco GNU/Linux | Ole-André Rodlie | — | 3-clause BSD License, GNU Lesser General Public License, version 2.1, GNU General Public License, version 2.0 |
| Dracos | — | — | — |
| DragonFly BSD | Matthew Dillon | 2003 | BSD licenses |
| Dragora GNU/Linux-libre | — | — | GNU General Public License |
| Dreamcast system software | Sega | — | — |
| Dreamlinux | — | — | GNU General Public License |
| DreamShell | — | — | BSD licenses |
| Droidian | — | — | — |
| DRYOS | Canon Inc. | — | proprietary license |
| DSLinux | — | — | GNU General Public License |
| DSOS | Texas Instruments | — | — |
| DuinOS | — | — | GNU General Public License |
| Dusk OS | — | — | GNU General Public License, version 3.0 |
| DuZeru | — | — | — |
| DX-DOS | — | — | — |
| DX10 | Texas Instruments | — | — |
| Dynebolic | — | — | GNU General Public License |
| Dynix | Sequent Computer Systems, IBM | — | — |
| Dyson | — | 2012 | — |
| E/OS | — | — | GNU General Public License, version 2.0 |
| EasyNAS | — | — | — |
| EasyOS | — | — | — |
| EasyPeasy | — | — | GNU General Public License |
| EComStation | XL Software Europe | — | proprietary license |
| ECos | — | — | eCos-2.0 |
| Edos | The Computer Software Company | — | — |
| Edubuntu | Canonical Ltd. | — | GNU General Public License |
| EducaAndOS | — | — | — |
| Educanix | — | — | GNU General Public License |
| Eduknoppix | — | — | GNU General Public License |