Open Source Real-Time Operating Systems

Zephyr is a scalable, security-focused real-time operating system (RTOS) designed for resource-constrained devices across multiple hardware architectures. It features a modular, small-footprint kernel with an extensive suite of subsystems, including a native networking stack, comprehensive Bluetooth Low Energy support, and a robust device driver model.

RT-Thread is a modular, object-oriented real-time operating system (RTOS) designed for both resource-constrained microcontrollers and high-performance IoT devices. It provides a scalable architecture ranging from a 3KB footprint kernel to a comprehensive IoT OS featuring a vast ecosystem of over 450 software packages and standardized interfaces like POSIX and CMSIS.

FreeRTOS is a market-leading real-time operating system kernel designed for microcontrollers and small microprocessors, featuring a small memory footprint and fast execution times. It provides a comprehensive ecosystem of libraries for IoT connectivity, security, and over-the-air updates, supporting over 40 processor architectures including ARM and RISC-V.

Tock is a secure, concurrent embedded operating system designed for ARM Cortex-M and RISC-V microcontrollers, prioritizing isolation between the kernel, device drivers, and applications. It leverages Rust's memory safety for its kernel and hardware Memory Protection Units (MPUs) to run multiple mutually distrustful applications on resource-constrained hardware with as little as 64kB of RAM.

TobudOS (formerly TencentOS Tiny) is a highly tailorable, open-source real-time operating system designed specifically for resource-constrained IoT terminal devices. It features a compact micro-kernel with a minimal footprint, advanced low-power management, and integrated connectivity stacks for seamless cloud integration.

RIOT is a modular, open-source real-time operating system specifically engineered for the Internet of Things (IoT), supporting a wide range of 8-bit, 16-bit, and 32-bit microcontrollers. It features a micro-kernel architecture with a preemptive, tickless scheduler and provides a uniform API with partial POSIX compliance to simplify cross-platform development and code reuse.

seL4 is a high-assurance, high-performance microkernel that is the first of its kind to be formally verified for functional correctness and security properties. It serves as a minimal core for building secure and reliable operating systems by enforcing strict isolation through a capability-based access control system.

Huawei LiteOS is a lightweight open-source IoT OS and a smart hardware development platform. It simplifies IoT device development and device connectivity, makes services smarter, delivers superb user experience, and provides better data protection. Huawei LiteOS is designed for smart homes, wearables, IoV, and intelligent manufacturing applications.

Arm Mbed OS is an open-source real-time operating system specifically designed for IoT applications on Arm Cortex-M microcontrollers. It provides a comprehensive platform integrating a deterministic RTOS kernel, multi-layered security foundations, and extensive connectivity stacks for wireless and wired networking.

AliOS Things is designed for low power, resource constrained MCU, connectivity SoC, greatly suitable for IoT devices. AliOS Things is not just a RTOS, it contains full stack of software components and tools for building IoT devices.

Apache NuttX is a highly scalable, standards-compliant real-time operating system (RTOS) designed for deeply embedded environments ranging from 8-bit to 64-bit architectures. It distinguishes itself by strictly adhering to POSIX and ANSI standards, providing a familiar Unix-like programming interface while maintaining a minimal footprint and modular architecture.

Contiki is a lightweight, open-source operating system designed for resource-constrained microcontrollers in the Internet of Things (IoT). It features a modular, event-driven architecture that supports standardized low-power wireless communication protocols while maintaining an extremely small memory footprint.

Hubris is a memory-isolated, task-based RTOS written in Rust, specifically designed for deeply-embedded microcontrollers with high reliability requirements. It eliminates dynamic resource allocation and runtime task creation to minimize attack surfaces and ensure deterministic behavior in critical systems.

Eclipse ThreadX is an industrial-grade real-time operating system (RTOS) featuring a non-layered picokernel architecture designed for deeply embedded, resource-constrained IoT applications. It provides deterministic scheduling, advanced multicore support through Symmetric Multiprocessing (SMP), and optional memory protection via a modular deployment system.

Mongoose OS is a modular IoT firmware development framework designed for microcontrollers, enabling rapid development in both C/C++ and JavaScript. It provides a comprehensive environment for connected devices with built-in support for secure OTA updates, remote management via a robust RPC mechanism, and native integration with major cloud providers like AWS IoT and Google IoT Core.

RTIC (Real-Time Interrupt-driven Concurrency) is a hardware-accelerated Rust RTOS designed for building real-time systems with minimal software overhead. It leverages the hardware's interrupt controller to manage task scheduling and utilizes the Stack Resource Policy (SRP) to provide compile-time guarantees for deadlock-free execution and data race free memory sharing.

CMSIS is a set of tools, APIs, frameworks, and workflows designed to simplify software re-use, reduce the learning curve for microcontroller developers, and accelerate project build and debug processes. It was initiated as a vendor-independent hardware abstraction layer for Arm® Cortex®-M based processors and later expanded to support entry-level Arm Cortex-A based processors. CMSIS aims to provide a consistent approach to interface with peripherals, real-time operating systems, and middleware components.

Embox is a highly modular and configurable real-time operating system designed to execute Linux-compatible software on resource-constrained embedded systems and microcontrollers. It provides a POSIX-compliant environment, allowing developers to port complex desktop-grade libraries and applications like Qt, OpenCV, and PJSIP to platforms with limited RAM and ROM.

TinyOS is an open source, BSD-licensed operating system designed for low-power wireless devices, such as those used in sensor networks, ubiquitous computing, personal area networks, smart buildings, and smart meters.

Contiki-NG is an open-source, cross-platform operating system designed for next-generation IoT devices, focusing on dependable, low-power communication. It provides a full, RFC-compliant IPv6 networking stack and supports modern industrial standards such as 6LoWPAN, 6TiSCH, RPL, and CoAP for resource-constrained hardware.

QP/C is a lightweight, event-driven real-time event framework (RTEF) based on the Active Object (Actor) model of computation and Hierarchical State Machines. It serves as a modern alternative to traditional RTOSs by providing a non-blocking, asynchronous architecture designed for deterministic execution in safety-critical embedded systems.

µC/OS-III is a highly portable, ROMable, scalable, preemptive, real-time, deterministic, multitasking kernel for microprocessors, microcontrollers and DSPs.

MuditaOS is an open-source mobile operating system built on FreeRTOS, specifically optimized for devices with E Ink displays such as the Mudita Pure phone and Mudita Harmony alarm clock. It features a modular architecture designed for low-distraction environments, integrating a custom GUI framework, a hardware abstraction layer, and various communication stacks for cellular and Bluetooth connectivity.

Apache Mynewt OS is a real-time, modular operating system for connected IoT devices that need to operate for long periods of time under power, memory, and storage constraints. It provides a complete environment for prototyping, developing, and managing em

ChibiOS is a modular, high-performance development environment for embedded systems, featuring a dual-kernel architecture with the full-featured RT kernel and the ultra-compact NIL kernel. It provides a comprehensive Hardware Abstraction Layer (HAL), a Virtual File System (VFS), and advanced sandboxing capabilities, making it highly suitable for functional safety and multicore ARM Cortex-M applications.

F9 microkernel is a microkernel-based (L4-style) kernel to support running real-time and time-sharing applications (for example, wireless communications) for ARM Cortex-M series microprocessors with efficiency (performance + power consumption) and security (memory protection + isolated execution) in mind.

Trampoline is a static RTOS for small embedded systems. Its API is aligned with OSEK/VDX OS and AUTOSAR OS 4.2 standards.

μC/OS-II is a portable, ROMable, scalable, preemptive, real-time deterministic multitasking kernel for microprocessors, microcontrollers and DSPs.

TizenRT is a lightweight, RTOS-based platform designed for low-end IoT devices with limited resources, typically equipped with ARM Cortex-M/R processors and less than 2MB of RAM. It extends the NuttX kernel with a comprehensive ecosystem including Linux-style development environments, advanced networking stacks, and support for high-level languages like JavaScript to bridge the gap between RTOS efficiency and Linux-like developer experience.

RTEMS is an open source RTOS that supports open standard application programming interfaces such as POSIX. It is used in space flight, medical, networking and many more embedded devices.

Drone is an Embedded Operating System for writing real-time applications in Rust.

distortos is an object-oriented C++ RTOS for microcontrollers.

Atomthreads is a free, lightweight, portable, real-time scheduler for embedded systems.

Neptune OS is a microkernel-based operating system that implements a Windows NT personality on top of the seL4 microkernel. It executes the NT Executive as a userspace root task, providing a faithful implementation of the NT Native API and a driver model where device drivers run in isolated processes while communicating via seL4 IPC.

HeliOS is a lightweight, multitasking kernel designed for low-power embedded devices, offering both event-driven and cooperative multitasking models without traditional context switching. It provides a rich API for task management, inter-process communication, and memory management while maintaining a tiny footprint suitable for Arduino and ARM Cortex-M platforms.

QuarkTS is a simple non-Preemtive Real-Time OS with a quasi-static scheduler for embedded multi-tasking applications.

scmRTOS is tiny Real-Time Preemptive Operating System intended for use with Single-Chip Microcontrollers. scmRTOS is capable to run on tiny uCs with as small amount of RAM as 512 bytes. The RTOS is written on C++ and supports various platforms.

TNeo is a well-formed and carefully tested preemptive real-time kernel for 16- and 32-bits MCUs. It is compact and fast.

Frosted (Free POSIX OS for Tiny Embedded Devices) is a POSIX-compliant RTOS designed for ARM Cortex-M microcontrollers, providing a Unix-like environment with kernel/userland separation. It features a modular architecture with a Virtual File System (VFS), integrated networking via picoTCP, and support for Binary Flat (BFLT) executables.

StateOS is a high-performance, lightweight real-time operating system designed for deeply embedded microcontrollers, featuring a unique task model inspired by state machines. It provides extensive C++ standard library compatibility, including support for std::thread and synchronization primitives, while maintaining a small footprint suitable for 8-bit and 32-bit architectures.

The eChronos RTOS is a real-time operating system (RTOS) originally developed by NICTA and Breakaway Consulting Pty. Ltd. It is intended for tightly resource-constrained devices without memory protection.

A Reliable Real-Time Operating System & Application Framework.

Phoenix-RTOS is an open-source, microkernel-based, realtime operating system for resource constrained devices.

StratifyOS is a powerful embedded RTOS for the ARM Cortex M microcontrollers.

BeRTOS is a real time open source operating system supplied with drivers and libraries designed for the rapid development of embedded software.

Linmo is a lightweight, preemptive multi-tasking RTOS kernel designed as an educational showcase for resource-constrained systems. It features a shared address space model and a priority-based round-robin scheduler, specifically targeting the RISC-V architecture and QEMU emulation.

BRTOS is a lightweight preemptive real time operating system designed for low end microcontrollers.

DuinOS is a small multithreading real time operating system (RTOS), based on the FreeRTOS kernel, for Arduino compatible boards.

MOE is an event-driven scheduler system for 8/16/32-bit MCUs. MOE means "Minds Of Embedded system".

IntrOS is a lightweight, cooperative operating system designed for deeply embedded applications, featuring a task model inspired by state machine concepts. It provides a comprehensive suite of synchronization primitives and communication mechanisms while maintaining a small footprint suitable for 8-bit to 32-bit microcontrollers.

LibreRTOS is a portable single-stack Real Time Operating System. All tasks share the same stack, allowing a large number or tasks to be created even on architectures with low RAM, such as ATmega328P (2kB).

SuperTinyKernel™ RTOS (STK) is a high-performance, deterministic, bare-metal C++ real-time operating system designed for resource-constrained embedded systems. It features a rich set of scheduling strategies including hard real-time (HRT) with deadline enforcement, mixed-criticality adaptive scheduling, and full CMSIS-RTOS2 and FreeRTOS API compatibility, targeting ARM Cortex-M and RISC-V architectures.

RA3 RTOS is a lightweight, open-source real-time operating system specifically designed for embedded systems.

The hyperC OS is a real time-operating system (RTOS) designed for various IoT applications. All the designs are aimed at the optimization of ARM Cortex CPUs.

HuskEOS is a real-time operating system (RTOS) designed for embedded systems. It offers a priority-based preemptive scheduler and boasts impressive performance metrics, such as achieving 50,000 context switches per second on a Cortex-M4 configured at 16MHz.

The TOPPERS/ATK (Automotive Kernel) is a real-time operating system for automotive system control publicly released by the TOPPERS project.

Femto OS: RTOS for small MCU's like AVR.

Mark3 is a sophisticated, modern RTOS and application development platform, targeted towards a growing list of today's most compelling embedded devices.

Nut/OS is an intentionally simple RTOS for the ATmega128, which provides a minimum of services to run Nut/Net, the TCP/IP stack.

Prex is an open source, royalty-free, real-time operating system for embedded systems. It is designed and implemented for resource-constrained systems that require predictable timing behavior. The highly portable code of Prex is written in 100% ANSI C bas

RTAI is the RealTime Application Interface for Linux - which lets you write applications with strict timing constraints for your favourite operating system. The RTAI distribution includes RTAI-Lab, a tool chain to convert block diagrams into RTAI executab

uSmartX is a non-preemptive, multitasking, priority based RTOS.

Xenomai is a real-time development framework cooperating with the Linux kernel, in order to provide a pervasive, interface-agnostic, hard real-time support to user-space applications, seamlessly integrated into the GNU/Linux environment.