| HyperWRT | — | — | GNU General Public License |
| I5 OS | IBM | — | — |
| IBM 4680 OS | IBM | — | — |
| IBM 4690 OS | IBM, Toshiba | — | — |
| IBM 7090/94 IBSYS | IBM | 1960 | — |
| IBM 8100 DPCX | IBM | — | — |
| IBM 8100 DPPX | IBM | 1978 | — |
| IBM Academic Operating System | IBM | — | — |
| IBM Airline Control Program | IBM | 1968 | — |
| IBM AIX | IBM | 1986 | proprietary license |
| IBM Basic Programming Support | IBM | — | — |
| IBM CP-40 | Cambridge Scientific Center | — | — |
| IBM i | IBM | — | — |
| IBM PC DOS | IBM | 1981 | proprietary license |
| IBM System/34, 36 System Support Product | IBM | — | — |
| IBM TopView | IBM | — | proprietary license |
| IBM Workplace OS | IBM | — | — |
| IBuntu | — | — | — |
| Icaros Desktop | — | — | — |
| ICL VME | International Computers Limited | — | — |
| IDEDOS | — | 1996 | GNU General Public License, version 2.0 |
| Idris | P. J. Plauger | — | commercial software, proprietary license |
| Iglunix | — | — | Zero-clause BSD License |
| IGolaware Linux | — | — | — |
| Illumos | — | — | Common Development and Distribution License version 1.0 |
| IMagic OS | — | — | — |
| Imagineos | — | — | — |
| IMAX 432 | Intel | — | — |
| IMDOS | IMS Associates | — | — |
| IMOS | NCR Corporation | — | — |
| Impi Linux | — | — | — |
| Incognito | — | 2008 | GNU General Public License |
| Incompatible Timesharing System | Massachusetts Institute of Technology | — | GNU General Public License v3.0 or later |
| IndLinux | — | — | GNU Lesser General Public License, version 2.1 or later, GNU General Public License, version 2.0 |
| Inferno | Vita Nuova Holdings, Bell Labs | — | GNU Lesser General Public License, MIT License, GNU General Public License |
| InfinitiveOS | — | — | — |
| InfraLinux | — | — | — |
| Injector Linux | — | — | GNU General Public License |
| INK | — | — | — |
| INMOS | Institute of Electronic Control Machines | — | — |
| Inquisitor | — | — | GNU General Public License |
| Inspur K-UX | Inspur | — | — |
| Instant WebKiosk | — | — | — |
| Integrity | Green Hills Software | — | — |
| INtime | — | — | — |
| IodéOS | — | — | Apache Software License 2.0, GNU Affero General Public License, version 3.0 |
| IOS | Apple Inc. | 2007 | proprietary license |
| IOS 10 | Apple Inc. | 2016 | end-user license agreement |