| Element OS | — | — | — |
| Embeddable Linux Kernel Subset | — | — | GNU General Public License |
| Embox | — | — | 2-clause BSD License |
| Emdebian Grip | — | — | GNU General Public License |
| Emteria.OS | — | — | — |
| EmuELEC | — | — | — |
| EMUI | Huawei | — | proprietary license |
| EmuTOS | — | — | GNU General Public License, version 2.0 |
| EOS | ETA Systems | — | — |
| ERIKA Enterprise | — | — | GPL linking exception |
| Erythros | — | — | Unlicense |
| Essence | Nakst | — | MIT License |
| EU OS | — | — | — |
| Eumel | — | — | — |
| Event Driven Executive | IBM | — | — |
| EWS-UX | NEC | — | — |
| EXEC | International Computers Limited | — | — |
| EXOS | Enterprise Computers | — | — |
| ExtremeXOS | Extreme Networks | — | — |
| Feather Linux | — | — | — |
| Femto OS | — | — | GNU General Public License |
| FireballISO | Indy | — | — |
| Fiwix | — | — | — |
| Flame-Sim | — | — | — |
| FLEX | Technical Systems Consultants | — | — |
| FlexOS | Digital Research | — | — |
| Floppyfw | — | — | — |
| FMI/OS | — | — | GNU General Public License |
| FortiOS | Fortinet | — | — |
| FreeDOS | Jim Hall | 1998 | GNU General Public License |
| FreeDOS-32 | — | — | GNU General Public License, version 3.0 |
| Freedows OS | — | — | — |
| FreeSBIE | — | — | BSD licenses |
| FreeVMS | — | — | GNU General Public License, version 3.0 |
| Fuchsia | Google | — | Apache License, MIT License, 3-clause BSD License |
| Fully Automated Nagios | — | — | — |
| Funtouch OS | Vivo | — | — |
| FuryBSD | — | 2019 | BSD licenses |
| FUSS | — | — | GNU General Public License |
| Fuzix OS | Alan Cox | — | GNU General Public License, version 2.0 |
| FydeOS | — | — | — |
| Galileo | Acorn Computers | — | — |
| GalliumOS | — | — | — |
| GeckOS | — | — | GNU General Public License |
| Genera | Symbolics | — | — |
| General Comprehensive Operating System | General Electric | 1962 | proprietary license |
| Gentoo GNU/Hurd | — | 2026 | GNU General Public License, version 2.0 |
| Gentoo/Alt | — | — | — |