| LinVDR | — | — | — |
| Linvo | — | — | — |
| Lisa OS | Apple Inc. | — | — |
| LiteOS | — | — | GNU General Public License, 3-clause BSD License |
| Livermore Time Sharing System | Lawrence Livermore National Laboratory | — | — |
| LliureX | Generalitat Valenciana | — | GNU General Public License |
| LNX-BBC | — | — | — |
| Loc-OS | — | — | GNU General Public License, version 2.0 |
| LOCUS | University of California, Los Angeles | — | proprietary license |
| LogoDIDACT | — | — | — |
| Loong Arch Linux | — | — | — |
| Loongnix | Loongson Technology Co., Ltd. | — | — |
| LOUD | — | — | — |
| Luberri Linux | — | — | — |
| Lubuntu | Canonical Ltd. | — | GNU General Public License |
| Lunar Linux | — | — | GNU General Public License |
| LuneOS | — | — | Apache License |
| LUnix | — | — | GNU General Public License, version 2.0 |
| LuxOS | — | — | GNU General Public License v3.0 or later |
| LXLE Linux | — | — | — |
| Lycoris | — | — | — |
| LynxOS | Lynx Software Technologies | — | — |
| M0n0wall | — | — | BSD licenses |
| Mabox Linux | — | — | — |
| Mac OS 8 | Apple Inc. | — | proprietary license |
| Mac OS 9 | Apple Inc. | — | proprietary license |
| Mac OS X 10.0 | Apple Inc. | 2001 | — |
| Mac OS X 10.1 | Apple Inc. | 2001 | Apple Public Source License |
| Mac OS X 10.2 | Apple Inc. | 2002 | Apple Public Source License, end-user license agreement |
| Mac OS X Leopard | Apple Inc. | 2007 | Apple Public Source License, end-user license agreement |
| Mac OS X Lion | Apple Inc. | 2011 | Apple Public Source License |
| Mac OS X Panther | Apple Inc. | 2003 | — |
| Mac OS X Public Beta | Apple Inc. | — | — |
| Mac OS X Server 1.0 | Apple Inc. | — | — |
| Mac OS X Snow Leopard | Apple Inc. | 2009 | Apple Public Source License |
| Mac OS X Tiger | Apple Inc. | 2005 | — |
| MacDroid | — | — | — |
| MachTen | — | — | — |
| MacMach | Carnegie Mellon University | — | — |
| MacOS | Apple Inc. | 2001 | BSD licenses, proprietary license, Apple Public Source License |
| MacOS Big Sur | Apple Inc. | 2020 | proprietary license, Apple Public Source License |
| MacOS Catalina | Apple Inc. | 2019 | Apple Public Source License |
| MacOS Golden Gate | Apple Inc. | 2026 | — |
| MacOS High Sierra | Apple Inc. | 2017 | Apple Public Source License |
| MacOS Mojave | Apple Inc. | 2018 | Apple Public Source License |
| MacOS Monterey | Apple Inc. | 2021 | proprietary license, Apple Public Source License |
| MacOS Sequoia | Apple Inc. | — | — |
| MacOS Server | Apple Inc. | 1999 | proprietary license, commercial software |