| Operating system | Developer | First release | License |
|---|---|---|---|
| Gentoo Linux | — | — | GNU General Public License |
| HP Multi-Programming Executive | Hewlett-Packard | — | — |
| NetBSD | — | 1993 | BSD licenses |
| NeXTSTEP | NeXT | — | proprietary license |
| OpenBSD | OpenBSD Project, Theo de Raadt | — | ISC license |