Open-source alternatives to FreeRTOS

ToaruOS is an independent operating system built from the ground up without external dependencies. It features a custom x86-64 kernel that supports symmetric multiprocessing and paging, paired with a graphical windowing system and a dedicated bytecode interpreter for application logic. The system distinguishes itself by integrating an embedded Python environment for system-level development and a custom graphical interface that handles its own window composition and text rendering. It includes a compatibility layer for third-party application support and a system package manager for handling

This project is a technical reference and educational guide focused on the internal architecture of the Linux kernel. It serves as a low-level systems programming resource and documentation for operating system internals, detailing the implementation of core mechanisms within the kernel source code. The materials provide a detailed study of the Linux kernel, tracing behavior through actual C source and assembly. It specifically covers the progression from the bootloader and decompression to the final kernel entry point, alongside the management of hardware interrupts and symmetric multiproces

xv6 is a Unix-like educational operating system designed for teaching kernel concepts. It is implemented as an instructional kernel for x86 and RISC-V architectures, featuring a virtual memory manager and support for symmetric multiprocessing. The system is designed to demonstrate core OS principles through a simplified re-implementation of Unix Version 6. It provides a controlled environment for studying system calls, trap handling, and process lifecycles. Its capability surface covers process management, including scheduling and context switching, and memory management via page tables for

Embassy is an asynchronous framework for microcontrollers that provides a runtime for cooperative multitasking. It enables the execution of multiple concurrent tasks to maximize energy efficiency and CPU usage, utilizing an async executor that puts the processor to sleep when idle. The framework includes a comprehensive set of embedded components, featuring a hardware abstraction layer for peripherals like GPIO, SPI, I2C, and UART, alongside a TCP/IP network stack and a USB device stack. It also provides a Bluetooth Low Energy host stack for wireless communication and a bootloader framework t

RT-Thread is an IoT real-time operating system and embedded device kernel. It provides a lightweight execution environment for microcontrollers, combining a real-time kernel with a hardware abstraction layer to manage multi-threaded task scheduling and hardware resource allocation. The project is built as a modular framework that utilizes a package-based ecosystem. This allows for the integration of reusable software libraries and high-level services through a loosely coupled architecture. The system covers real-time task scheduling, resource-constrained memory management, and embedded hardw

RIOT is a real-time operating system designed for resource-constrained microcontrollers. It provides a kernel for managing hardware peripherals, memory, and multitasking on embedded devices, featuring a microcontroller hardware abstraction layer to unify hardware access across different chipsets. The system employs a preemptive tickless task scheduler with priority-based execution to maximize energy efficiency in battery-powered hardware. It also includes an embedded security framework consisting of cryptographic APIs and secure transport protocols to facilitate authenticated over-the-air fir

Tock is a secure embedded operating system and microcontroller kernel designed to isolate untrusted applications and drivers. It functions as a memory-safe process isolator that uses a combination of hardware memory protection and language-level type safety to execute mutually distrustful applications on bare metal. The system distinguishes itself through a hardware abstraction layer that decouples high-level components from specific microcontroller implementations using standardized traits. It further employs a virtualization layer to allow multiple independent software components to share a

Kotlinx.coroutines is a library for managing non-blocking background tasks and structured concurrency within the Kotlin programming language. It provides a framework for executing concurrent operations and synchronizing shared state, replacing traditional thread management and complex callback chains with lightweight primitives. The library utilizes a structured concurrency hierarchy to organize hierarchical background tasks, ensuring that lifecycle management, cancellation, and timeout handling propagate automatically to prevent resource leaks. It employs continuation-passing style transform

ZSWatch is a real-time operating system for wearable devices featuring a touch display and Bluetooth Low Energy connectivity. It provides a comprehensive software suite that includes a Bluetooth LE communication stack, an embedded UI framework for round displays, and a complete firmware toolchain for compiling, flashing, and simulating wearable hardware. The project is distinguished by its specialized wearable capabilities, such as a graphical framework for designing reactive screens and watchfaces via a visual editor. It implements a publish-subscribe messaging system to decouple hardware se

LiteOS is a lightweight real-time operating system kernel designed for constrained devices with limited memory and processing power. It provides a foundation for embedded IoT development, focusing on stable and predictable system resource management. The system implements a preemptive task scheduler and interrupt-driven resource management to ensure real-time responsiveness. It incorporates a tickless idle mechanism and optimized sleep-wake cycles to reduce power consumption in battery-powered hardware. The kernel includes capabilities for task synchronization via semaphores and static memor

This project is flight control autopilot software designed as a real-time operating system for managing the flight dynamics and navigation of autonomous multicopters, fixed-wing aircraft, and rovers. It serves as a multi-vehicle autopilot framework that supports various aircraft configurations, including vertical takeoff and landing platforms across industrial environments. The system includes a MAVLink communication stack for exchanging telemetry and command data between unmanned vehicles and ground control stations. It also provides a software-in-the-loop flight simulator to test autopilot

CPlusPlusThings is an educational and technical resource collection featuring C++ coding exercises, a concurrency library, and a programming guide. It provides structured drills and real-world challenges to reinforce language proficiency and offers technical analysis of the internal implementation of the standard library. The project implements software architecture patterns and industry-standard idioms, including the singleton pattern and resource acquisition is initialization. It also includes a framework for building logging systems with configurable severity levels and output destinations

Napajs is an embeddable JavaScript engine and multi-threaded runtime designed to be integrated directly into other software applications as a component. It serves as a parallel computation framework that allows JavaScript code to execute across multiple threads, bypassing the standard single-threaded event loop limitation to handle CPU-intensive tasks. The runtime is distinguished by its ability to load and execute modules from the NPM ecosystem and its pluggable execution environment. This architecture allows for custom implementations of memory allocation, system logging, and performance me

Sidekiq is a background job processor and queue manager for Ruby that uses Redis to manage asynchronous tasks. It functions as a distributed task scheduler capable of handling periodic, delayed, and recurring jobs across a cluster of worker processes. The project features a job monitoring dashboard and administrative web interface for visualizing system state, tracking worker performance, and managing failed or dead jobs. It provides a distributed rate limiter to control execution frequency across multiple processes. The framework covers a broad range of operational capabilities, including j

This project is a cross-platform mobile animation library and UI thread animation engine designed to create high-performance animations by running JavaScript logic directly on the UI thread. It functions as a multi-threaded JavaScript runtime that allows code to execute across multiple threads to improve concurrency and prevent frame drops. The library focuses on enabling fluid user interface interactions and high-frame-rate transitions that remain stable regardless of the main processing load. It provides a system for offloading animation logic from the main thread to ensure smooth motion an

This project is a comprehensive technical interview question bank and reference library designed for software engineering roles at major technology companies. It serves as a study guide and knowledge base covering the core principles of high-performance systems programming and computer science theory. The collection focuses on deep technical domains, including C++ language mastery, distributed systems design, and database engineering. It provides detailed material on consensus protocols, cluster coordination, and the architectural differences between SQL and NoSQL implementations. The resour

Sidekiq is a Ruby background processing framework and asynchronous task runner. It functions as a Redis-backed background job processor that offloads heavy or time-consuming work from web requests to separate worker processes to ensure the main application remains responsive. The system operates as a Redis task queue, storing pending jobs in Redis to be processed concurrently by multiple threads. It provides a framework for distributed task queueing and asynchronous job scheduling to coordinate work across multiple server instances. The project covers Ruby application scaling by executing ba

This project is a collection of minimal operating systems, bootloaders, and hardware drivers used to demonstrate low-level x86 system programming and hardware interfacing. It serves as a kernel development toolkit and a system programming lab designed for testing architecture concepts and hardware behavior within a system emulator. The repository provides reference implementations for creating bootable disk images and loading kernel stages. It includes guides for implementing protected mode transitions, memory paging, interrupt descriptor tables, and symmetric multiprocessing on x86 hardware.

This project is a Chinese translation and educational resource focused on the internal workings of the Linux kernel. It provides a curated collection of technical content designed for studying low-level operating system mechanisms and kernel development. The project utilizes a specialized localization workflow where translations are maintained in a forked repository. It employs a patch-based model and Git-driven synchronization to align Chinese translations with the original English source files through differential merge processes. The technical scope covers core operating system internals,

sysbench is a database and system benchmark tool used to measure the throughput and latency of database systems and hardware components. It functions as a multi-threaded workload generator and hardware performance profiler designed to determine how systems perform under heavy load. The project serves as a scriptable benchmark engine, allowing for the definition of custom performance scenarios through scripts. It simulates real-world traffic patterns by generating random data based on mathematical probability distributions, such as Zipfian, Gaussian, or Pareto. Capabilities cover database per

Flecs is a high-performance entity component system framework and data-oriented programming library. It serves as a simulation engine core and game engine architecture tool, decoupling state from behavior by separating entities, components, and systems. The framework features a runtime reflection layer for dynamic data inspection and a built-in scripting system for defining entity behavior without recompilation. It also includes a network interface and REST API for remote simulation administration and state querying. The library covers a broad surface of simulation capabilities, including ar

xv6-riscv is a simplified Unix-like teaching operating system designed for the study of kernel design and hardware interaction. It provides a low-level RISC-V kernel implementation that serves as a bootable system image for execution and debugging within a virtual machine or emulator. The project focuses on educational instruction regarding the RISC-V architecture. It enables the study of operating system concepts through a minimal kernel that implements process management and memory handling. The system covers core kernel operations including multiprocessor resource management and the imple

Mongoose is an embedded networking library providing TCP/IP stacks, web server hosting, and IoT device connectivity. It enables microcontrollers and desktop systems to implement network protocols including HTTP, WebSocket, and MQTT. The project provides a bare-metal TCP/IP stack for environments without a native operating system and includes built-in TLS and ECC encryption to secure network traffic. It features a binary-embedded file system to serve web content directly from the executable and supports over-the-air firmware updates for managing device fleets. Additional capabilities cover as

bgfx is a cross-platform, graphics rendering abstraction layer designed for high-performance applications. It provides a unified interface that maps high-level rendering commands to native graphics APIs, allowing developers to maintain a single codebase that executes consistently across diverse operating systems and hardware architectures. The library distinguishes itself through a multi-threaded command submission model that decouples rendering logic from the main application thread, effectively minimizing CPU bottlenecks. It utilizes a backend-agnostic command buffer and a deferred resource

JCTools is a Java concurrency library providing a collection of lock-less and wait-free data structures. It serves as a toolkit for managing thread-safe data exchange, specifically designed to optimize high-throughput messaging and producer-consumer patterns in multi-threaded applications. The library distinguishes itself by implementing specialized queue structures that minimize contention and maximize throughput. By utilizing techniques such as cache-line padding, memory-barrier-based synchronization, and relaxed-consistency memory ordering, it avoids the performance bottlenecks often assoc

Rust-analyzer is a language server implementation that provides real-time code intelligence, static analysis, and development productivity tools for the Rust programming language. It functions as a backend engine that communicates with text editors to deliver deep structural understanding of source code, enabling features like semantic analysis, symbol navigation, and automated refactoring. The project distinguishes itself through a core engine designed for high-performance responsiveness, utilizing incremental query-based compilation and lazy demand-driven evaluation to minimize resource con

OpenCV is a comprehensive computer vision library designed for real-time performance and cross-platform deployment. It provides a native execution environment that leverages multi-threaded operations and automated memory management to handle intensive computational tasks, including image processing and machine learning model inference. The library distinguishes itself through a data-oriented matrix framework that utilizes proxy-based array abstractions to provide a consistent interface for multidimensional data. By employing factory-pattern algorithm interfaces and runtime type dispatching, i