Open Source Real-Time Operating Systems

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.

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.

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.

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.

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.

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.

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.

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.