Phoenix-RTOS is a scalable, open-source, real-time operating system designed for IoT devices and other resource-constrained applications. It features a custom microkernel architecture, separating core functionalities like memory management, scheduling, and IPC from higher-level services such as filesystems, networking stacks, and device drivers, which run as server processes in user space. This design emphasizes modularity and scalability, allowing deployment on microcontrollers up to multi-processor systems. It supports multiple hardware architectures including ARM Cortex-M/A, x86, RISC-V, and SPARC (LEON).

Tock is an embedded operating system designed for running multiple concurrent, mutually distrustful applications on ARM Cortex-M and RISC-V microcontrollers. Its core design prioritizes safety and reliability, utilizing Rust’s compile-time guarantees to protect the kernel and drivers, and hardware Memory Protection Units (MPUs) to isolate applications. Tock introduces a unique architecture dividing components into kernel-space “capsules” (Rust-based, cooperatively scheduled, minimal overhead) and user-space “processes” (MPU-isolated, preemptively scheduled, can be written in any language and loaded dynamically). This approach enables robust, secure applications on resource-constrained devices like wearables and IoT nodes.

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

MaRTE OS is a Hard Real-Time Operating System for embedded applications that follows the Minimal Real-Time POSIX.13 subset.

modm is a toolbox for building custom C++17 libraries tailored to your embedded device. modm generates startup code, HALs and their implementations, communication protocols, drivers for external devices, BSPs, etc… in a modular, customizable process that you can fine-tune to your needs.

Arduino True Color Library for TFTs and OLEDs

A lean and efficient Python implementation for microcontrollers and constrained systems.

cocoOS is a free, open source, cooperative task scheduler, based on coroutines targeted for embedded microcontrollers like AVR, MSP430 and STM32.

lwIP is a small independent implementation of the TCP/IP protocol suite. The focus of the lwIP TCP/IP implementation is to reduce resource usage while still having a full scale TCP. This makes lwIP suitable for use in embedded systems with tens of kilobytes of free RAM and room for around 40 kilobytes of code ROM.

JesFs is an Ultra-Lightweight Flash File System, especially designed for NOR-Flash.

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

TizenRT is a lightweight Real-Time Operating System (RTOS) developed by Samsung, designed to extend the Tizen platform to low-end, resource-constrained IoT devices. Based initially on the NuttX kernel, TizenRT targets microcontrollers like ARM Cortex-M/R with limited memory (less than 2MB RAM) and flash storage (less than 16MB). It provides a familiar Linux-like development environment with POSIX API compatibility, BSD sockets, and a shell interface (TASH). TizenRT includes integrated networking stacks (IPv4/IPv6), file systems, a lightweight database (AraStorage), and support for various IoT protocols, aiming to simplify development for connected devices.

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.

OpenThread released by Nest is an open-source implementation of the Thread networking protocol.

Mongoose OS is an open-source IoT firmware development framework designed for resource-constrained microcontrollers like ESP32, ESP8266, STM32, and TI CC32xx series. It enables rapid development with support for both C/C++ and JavaScript (via its embedded mJS engine). Key features include reliable Over-the-Air (OTA) updates with rollback, built-in security features like flash encryption and TLS, and seamless integration with major cloud platforms (AWS IoT, Google Cloud IoT, Azure IoT) and MQTT servers. It comes with the mos command-line tool for simplified building, flashing, and device management.

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.

LVGL is the most popular free and open-source embedded graphics library to create beautiful UIs for any MCU, MPU and display type.

A little fail-safe filesystem designed for embedded systems

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.

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