ChibiOS Real-Time OS

Complete development environment for embedded real-time systems

Contiki-NG RTOS

Open source real-time operating system for Next Generation IoT

eCos Real-Time Operating System

Open source configurable embedded real-time operating system

Embedded Linux RTOS ThreadX

Advanced industrial grade real-time operating system framework

EmBOX Embedded RTOS

Configurable OS designed for real-time embedded applications

Erika Enterprise RTOS

OSEK/VDX certified hard real-time operating system kernel

FreeRTOS Real-Time Kernel

Market leading open source real-time operating system kernel

μC/OS-III Real-Time Kernel

Preemptive real-time kernel with deterministic execution execution

NuttX Real-Time Operating System

Standards-conforming real-time OS for microcontrollers

POSIX Real-Time Systems Profile Standard

IEEE Std 1003.13 standard profile for real-time operating systems

QNX Real-Time Operating System

Commercial deterministic real-time operating system microkernel

Real-Time Control Systems Library -- Software and Documentation | NIST

The Real-Time Control Systems library is an archive of free C++, Java and Ada code, scripts, tools, makefiles, and documentation developed to aid programmers of software to be used in real-time control systems

RIOT Operating System

The friendly Operating System for the Internet of Things RTOS

RT-Linux Kernel Wiki

PREEMPT_RT real-time architecture patchset for the Linux kernel

RT-Thread Embedded RTOS

Open source real-time operating system for IoT and embedded devices

SciCOS Real-time Simulator

Toolbox for modeling and real-time simulation of dynamic systems

T-Kernel Real-Time Platform

Real-time operating system specification by TRON Forum

TOPPERS Real-Time OS Japan

Open source real-time operating system specifications and software

Wind River VxWorks RTOS

Industry-leading real-time operating system for embedded systems

Xenomai Real-Time Framework

Real-time development framework seamlessly integrated with Linux

Zephyr RTOS Project

Scalable real-time operating system optimized for embedded devices