QP/C is a lightweight, open-source Real-Time Event Framework (RTEF) for building responsive and modular real-time embedded applications in C. It implements the Active Object (Actor) model of computation and utilizes Hierarchical State Machines (HSMs) to describe system behavior. QP/C promotes asynchronous, event-driven programming, enhancing safety and maintainability compared to traditional RTOS approaches based on shared-state concurrency and blocking calls. It can run standalone on bare-metal MCUs or be deployed on top of various 3rd-party RTOS and OSes.

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

Apex is a real-time operating system (RTOS) designed for use in small to medium scale embedded systems. It aims to be a bridge between traditional RTOSes for small microcontrollers and Linux for larger embedded systems. Apex provides a Linux-compatible environment, making it easier for developers familiar with Linux. The RTOS is currently under heavy development and is not considered stable.

Features

#

• Implements a subset of the Linux syscall interface.
• Uses the musl C library.
• Monolithic architecture (as opposed to microkernel).
• Open source & royalty-free.
• Secure & reliable.
• Small, efficient, and easy to understand.
• Binary compatibility with Linux (using musl libc).
• Development can focus on the kernel as userspace tools & libraries are provided by external projects.

Components

#

• Boot Loader: Responsible for initializing the system and loading the kernel.
• CPU: Contains CPU-specific configurations and sources.
• Libc: C library for the bootloader and kernel.
• Libc++: C++ library for the bootloader and kernel.
• Machine: Contains machine/board support files.
• MK: Build system.
• Sys: Apex kernel which includes:
  • Architecture support.
  • Device drivers.
  • File systems.
  • Kernel core.
  • Memory management.
  • Synchronization primitives.

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.

Hubris is a microcontroller operating system designed for deeply embedded systems prioritizing reliability and robustness. Developed in Rust, it leverages memory safety features and strict memory isolation using the Memory Protection Unit (MPU) found on target MCUs like ARM Cortex-M. Tasks run in unprivileged mode and communicate via synchronous IPC. Hubris employs a static task model, where tasks are defined at compile time, enhancing predictability and simplifying resource management. It features a unique supervisor task responsible for managing other tasks and handling faults. Development utilizes a custom xtask-based build system and integrates tightly with the Humility debugger.

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.

Eclipse ThreadX is an advanced, widely deployed Real-Time Operating System (RTOS) designed for deeply embedded, real-time, and IoT applications, especially on resource-constrained devices. Formerly known as Azure RTOS, ThreadX offers reliable, ultra-fast performance with a minimal footprint (as low as 2KB ROM, 1KB RAM). It features a picokernel architecture, preemption-threshold scheduling, event chaining, comprehensive IPC mechanisms, and a rich ecosystem including networking, file system, USB, and GUI components. ThreadX comes with extensive safety and security certifications (e.g., TÜV IEC 61508 SIL4, UL 60730, EAL4+, FIPS 140-2).

Contiki-NG is an operating system for resource-constrained devices in the Internet of Things. Contiki-NG contains an RFC-compliant, low-power IPv6 communication stack, enabling Internet connectivity.

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

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

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

TencentOS tiny is a real-time operating system developed by Tencent for the Internet of Things. It features low power consumption, low resource consumption, modularity, security and reliability, and can effectively improve the development efficiency of IoT terminal products.

This an experimental port of TensorFlow Lite aimed at micro controllers and other devices with only kilobytes of memory.

uTensor is an extremely light-weight machine learning inference framework built on Mbed and Tensorflow. It consists of a runtime library and an offline tool. The total size of graph definition and algorithm implementation of a 3-layer MLP produced by uTensor is less than 32kB in the resulting binary (excluding the weights).

Features

#

• Convolution
• Pooling
• CMSIS-NN integration
• Smaller binary
• More efficient Run-time

Resources

#

• utensor_cgen. C++ code generator for uTensor https://utensor-cgen.readthedocs.io/en/latest/.
• oscw18-edge-ai. Analysys of edge computing resources for cubesats.
• utensor-mnist-demo. Handwritten digit recognition demo.

Apache NimBLE is an open-source Bluetooth 5.0 stack (both Host & Controller) that completely replaces the proprietary SoftDevice on Nordic chipsets. It is part of Apache Mynewt project.

EasyFlash is an open source lightweight embedded flash memory library. It provides convenient application interface for MCU. The developers can achieve more efficient and common application development based on Flash memory.

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

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.

Frosted is an acronym that means “Free Operating Systems for Tiny Embedded Devices”. The goal of this project is to provide a Free (as in Freedom) kernel for embedded systems, which exposes a POSIX-compliant system call API.

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.