| /e/OS | Gaël Duval, E Foundation | 2018 | MIT License, Apache Software License 2.0 |
| 386BSD | William Jolitz, Lynne Jolitz | 1992 | BSD licenses |
| 3CX Phone System | — | — | end-user license agreement |
| 4K Disk Monitor System | Digital Equipment Corporation | — | — |
| 4MLinux | — | — | — |
| 64 Studio | — | — | GNU General Public License |
| 68K/OS | GST Computer Systems | — | — |
| 86-DOS | Seattle Computer Products, Tim Paterson | 1980 | — |
| 9front | — | — | MIT License |