| B2G OS | — | — | Mozilla Public License |
| BackBox | — | — | GNU General Public License |
| BackSlash Linux | Kumar Priyansh | — | Apache Software License 2.0 |
| BackTrack | — | 2006 | GNU General Public License |
| Bada | Samsung Electronics | — | proprietary license |
| Baidu Yi | Baidu | — | — |
| Baltix | — | — | GNU General Public License |
| Bankix | — | — | — |
| Banyan VINES | Banyan Systems | — | — |
| BareMetal | — | — | BSD licenses |
| Barrelfish | — | — | MIT License |
| BasicLinux | — | — | — |
| Batocera.linux | — | — | GNU General Public License |
| Bazzite | — | — | Apache Software License 2.0 |
| BeatrIX | — | — | — |
| Bedrock Linux | — | — | GNU General Public License, version 2.0 |
| Behördendesktop | Federal Office for Information Security | — | — |
| BeleniX | — | — | Common Development and Distribution License version 1.0 |
| BengalOS | — | — | — |
| BeOS | Be Inc., Jean-Louis Gassée, Cyril Meurillon, Jean-Baptiste Maurice Quéru, Benoit Schillings, Dominic Giampaolo, Steve Sakoman | — | proprietary license |
| BeOS R5.1d0 | Be Inc. | — | — |
| Berkeley Software Distribution | University of California, Berkeley | — | BSD licenses |
| Berkeley Timesharing System | University of California, Berkeley | — | — |
| Berry Linux | — | — | — |
| BeRTOS | — | — | GNU General Public License, version 2.0 or later |
| BESYS | Bell Labs | — | — |
| Bharat Operating System Solutions | Centre for Development of Advanced Computing | — | GNU General Public License |
| BharOS | Indian Institute of Technology Madras | — | — |
| Bifrost | — | — | — |
| Big Linux | Bruno Gonçalves | — | — |
| Binary Runtime Environment for Wireless | Qualcomm | — | — |
| BinToo GNU / Linux | — | — | — |
| BioSLAX | National University of Singapore | — | — |
| Bitrig | — | — | ISC license |
| BKUNIX | Sergey Vakulenko | — | — |
| Black Lab Linux | — | — | — |
| BlackArch Linux | — | — | 3-clause BSD License |
| BlackBerry 10 | BlackBerry | — | proprietary license |
| BlackBerry OS | BlackBerry | 1999 | proprietary license |
| BlackBerry Tablet OS | BlackBerry | — | — |
| BlackPanther OS | — | — | — |
| BLAG Linux and GNU | — | — | GNU General Public License |
| BlankOn | — | — | — |
| BlendOS | — | — | — |
| BLIS/COBOL | — | — | — |
| Bliss OS | — | — | GNU General Public License, version 3.0 |
| Bluefin | — | — | — |
| Bluewhite64 | — | — | — |
| BluOS | NAD Electronics | — | — |
| Bodhi Linux | — | — | GNU General Public License |
| Bonzai Linux | — | — | — |
| Boot-root | H J Lu | — | — |
| BOS/360 | IBM | — | proprietary license |
| BrickOS | — | — | — |
| Bridge Linux | — | — | GNU General Public License |
| BridgeOS | Apple Inc. | — | proprietary license |
| BRTOS | — | — | — |
| BS2000 | Fujitsu Technology Solutions | 1975 | — |
| BSD | — | — | — |
| BSD Router Project | — | — | BSD licenses |
| BSD/OS | Berkeley Software Design | — | — |
| Buenos | — | — | — |
| Buildix | ThoughtWorks | — | — |
| Bullx SCS | Atos SE | — | — |
| BunsenLabs | — | 2015 | — |
| Burroughs MCP | Burroughs Corporation | 1961 | — |