| AmigaOS | Hyperion Entertainment, Haage & Partner, Commodore International | — | end-user license agreement |
| AmigaOS 4 | Hyperion Entertainment | 2006 | proprietary license |
| AmiKit | — | — | proprietary license |
| Amoeba | Andrew S. Tanenbaum | — | MIT License |
| AmogOS | — | — | 4-clause BSD License |
| AmonEcole | EOLE | — | — |
| AMSDOS | Amstrad | — | — |
| Analogue OS | Analogue Inc. | — | — |
| ANDOS | — | — | — |
| Android | Google | — | Apache Software License 2.0, GNU General Public License, version 2.0 |
| Android 1.0 | — | — | Apache Software License 2.0 |
| Android 1.1 | — | 2009 | — |
| Android 10 | Google, Open Handset Alliance | 2019 | Apache License |
| Android 11 | Open Handset Alliance | — | — |
| Android 12 | Google | — | proprietary license |
| Android 13 | Open Handset Alliance, Google | — | — |
| Android 14 | Google | — | — |
| Android 15 | Google | — | — |
| Android 16 | Google, Open Handset Alliance | — | — |
| Android 17 | Android Jetpack, Open Handset Alliance | — | — |
| Android Auto | Google | 2015 | proprietary license |
| Android Automotive | — | 2017 | — |
| Android Canary | — | 2025 | — |
| Android Cupcake | Google | — | — |
| Android Donut | Google | — | — |
| Android Eclair | Google | — | — |
| Android Froyo | Google | — | — |
| Android Gingerbread | Google | 2010 | — |
| Android Go | — | 2017 | — |
| Android Honeycomb | Google | — | — |
| Android Ice Cream Sandwich | Google | — | — |
| Android Jelly Bean | Google | — | — |
| Android KitKat | Open Handset Alliance, Google | — | Apache License, GNU General Public License |
| Android Lollipop | — | 2014 | Apache Software License 2.0, Android Open Source Project, GNU General Public License, version 2.0 |
| Android Marshmallow | Open Handset Alliance, Google | — | free software, Android Open Source Project |
| Android Nougat | Google, Open Handset Alliance | 2016 | Android Open Source Project |
| Android on Raspberry Pi | — | — | — |
| Android Open Source Project | — | — | Creative Commons Attribution 2.5 Generic, GNU General Public License, Apache License |
| Android Oreo | Google, Open Handset Alliance | 2017 | Android Open Source Project, Apache License |
| Android Pie | Google, Open Handset Alliance | 2018 | Apache License |
| Android Things | — | — | Apache License |
| Android TV | Google | 2014 | proprietary license |
| Android XR | Google, Samsung Electronics | — | — |
| Android-x86 | — | 2017 | Apache License |
| AnduinOS | — | — | GNU General Public License, version 3.0 |
| Annvix | — | — | — |
| Antergos | — | 2013 | GNU General Public License |
| Anthon OS | — | — | — |