| BRTOS | — | — | — |
| CD-RTOS | — | — | — |
| ChibiOS/RT | — | — | Apache Software License 2.0, GNU General Public License, version 3.0 |
| ChorusOS | Chorus Systèmes, Oracle Corporation, Sun Microsystems, Institut National de Recherche en Informatique et en Automatique | — | BSD licenses, GNU Lesser General Public License, Mozilla Public License, Sun Public License |
| DICOS | Ericsson | — | — |
| DRYOS | Canon Inc. | — | proprietary license |
| ERIKA Enterprise | — | — | GPL linking exception |
| FreeRTOS | — | 2003 | MIT License |
| Fuchsia | Google | — | Apache License, MIT License, 3-clause BSD License |
| Integrity | Green Hills Software | — | — |
| JetOS | Institute for System Programming, State Research Institute of Aviation Systems | — | — |
| LiteOS | — | — | GNU General Public License, 3-clause BSD License |
| LynxOS | Lynx Software Technologies | — | — |
| MaRTE OS | University of Cantabria | — | GNU General Public License, version 2.0 |
| Nucleus RTOS | Mentor Graphics | — | — |
| Nut/OS | Ethernut | 2000 | BSD licenses |
| NuttX | Apache Software Foundation | — | Apache License, Apache Software License 2.0 |
| OSEck | ENEA AB | — | — |
| PEARL Operating System | Brown, Boveri & Cie | — | — |
| PX5 RTOS | William Lamie | — | — |
| RDOS | Data General | — | — |
| RIOT | Martin Lenders, Benjamin Valentin, Alexandre Abadie | — | GNU Lesser General Public License, version 2.1 |
| RT-Thread | — | — | Apache Software License 2.0 |
| RTEMS | Sebastian Huber, Joel Sherrill | — | GNU General Public License |
| Special Real Time Operating System | IBM | — | — |
| ThreadX | — | — | MIT License |
| Versatile Real-Time Executive | Jim Ready | — | — |
| VxWorks | Wind River Systems | — | end-user license agreement |
| XTOS | Tensilica | — | — |
| Zephyr | Wind River Systems, Linux Foundation | — | Apache Software License 2.0 |