| AmigaOS | Hyperion Entertainment, Haage & Partner, Commodore International | — | end-user license agreement |
| AROS Research Operating System | — | — | AROS Public License |
| ChorusOS | Chorus Systèmes, Oracle Corporation, Sun Microsystems, Institut National de Recherche en Informatique et en Automatique | — | BSD licenses, GNU Lesser General Public License, Mozilla Public License, Sun Public License |
| Classic Mac OS | Apple Inc. | — | — |
| Fuzix OS | Alan Cox | — | GNU General Public License, version 2.0 |
| OpenWrt | Gábor Juhos, Florian Fainelli, Hauke Mehrtens, Jo-Philipp Wich | 2004 | GNU General Public License, version 2.0 |
| RTEMS | Sebastian Huber, Joel Sherrill | — | GNU General Public License |
| UCSD p-System | — | — | — |
| ΜnOS | — | — | — |