| Haansoft Linux | — | — | — |
| Hacao | — | — | — |
| Hackable:1 | — | — | — |
| Haiku | Michael Phipps, Haiku Inc. | 2002 | MIT License |
| Halium | — | — | — |
| HamoniKR | — | — | — |
| HandyLinux | — | — | GNU General Public License |
| Hanthana Linux | — | — | GNU General Public License |
| Happy MacLinux | — | — | — |
| HardenedBSD | — | — | — |
| Harmony (operating system) | — | — | — |
| HarmonyOS | Huawei | 2019 | — |
| HarmonyOS NEXT | Huawei | 2023 | — |
| Harvey OS | — | — | GNU General Public License, version 2.0, Lucent Public License |
| HDOS | Heath Company, Gordon Letwin | — | — |
| HelenOS | — | — | 3-clause BSD License |
| HeliOS | Perihelion Software | — | — |
| HelloSystem | — | — | — |
| HI-UX | Hitachi | 1987 | — |
| Hikarunix | — | — | — |
| Hiren's BootCD | — | — | freeware |
| Hitachi VOS | Hitachi | — | — |
| Home Assistant OS | — | — | Apache Software License 2.0 |
| HomeOS | Apple Inc. | — | — |
| HomeOS | Microsoft | — | — |
| Honeywell CP-6 | Honeywell | — | — |
| House | — | — | BSD licenses |
| HP Multi-Programming Executive | Hewlett-Packard | — | — |
| HP-UX | Hewlett Packard Enterprise | 1984 | proprietary license |
| HPE Cray Operating System | — | — | — |
| Huayra Linux | — | — | GNU General Public License |
| Hybryde Linux | — | — | — |
| Hyperbola GNU/Linux-libre | — | — | — |
| HyperSpace | Phoenix Technologies | — | — |
| HyperWRT | — | — | GNU General Public License |