When it comes to real-time operating systems (RTOS) in the embedded world, Zephyr and FreeRTOS stand out as two of the most prominent options. Both are open-source, widely adopted, and continuously evolving. Yet, they serve different needs depending on complexity, scalability, and ecosystem requirements. Here’s a detailed comparison to help you decide which might be right for your project.
Overview
- FreeRTOS: Lightweight, simple, and designed for microcontrollers with very limited resources. Originally developed by Real Time Engineers Ltd., it is now maintained by Amazon with tight AWS IoT integration. The latest release, V11.2.0 (March 2025), adds support for new devices like Renesas F1Kx.
Official FreeRTOS site - Zephyr: A Linux Foundation project with broad industry backing. Zephyr is a full-featured RTOS with networking, drivers, security, and modular components for complex IoT and industrial systems. The latest Version 4.1 (March 2025) introduced new features and developer improvements.
Official Zephyr site
Advantages and Disadvantages
FreeRTOS
Advantages:
- Extremely lightweight (~10 KB RAM/ROM).
- Easy to learn with clear documentation.
- Confirmed as the most widely deployed RTOS in 2025.
- Tight integration with AWS IoT and cloud ecosystems.
Disadvantages:
- Provides only basic scheduling and synchronization primitives.
- Lacks built-in networking, filesystems, or advanced security.
- Complex IoT products require significant add-ons.
Zephyr
Advantages:
- Comprehensive ecosystem: networking (Bluetooth, Wi-Fi, 6LoWPAN, LoRa), USB, filesystems, OTA updates.
- Multi-architecture support (ARM, x86, ARC, RISC-V, etc.).
- Strong focus on security: memory protection, secure boot, CVE tracking.
- Vendor-neutral governance ensures long-term stability.
- Ongoing focus on developer onboarding improvements.
Disadvantages:
- Higher complexity compared to FreeRTOS.
- Steeper learning curve.
- Larger footprint (>50 KB RAM/ROM depending on configuration).
Best Applications
- FreeRTOS: Small MCUs, simple sensors, low-power nodes, or projects where AWS integration is key.
- Zephyr: Connected wearables, industrial IoT, smart home hubs, and secure low-power devices that require OTA updates and advanced networking.
Long-Term Future
- FreeRTOS: Stable, widely deployed, and continuously integrated into STM32 and AWS ecosystems. With recent USBX, FileX, and LWIP integrations, it’s regaining traction as a preferred kernel in some vendor stacks.
- Zephyr: Rapid adoption across the industry. Backed by Intel, Nordic Semiconductor, NXP, and the Linux Foundation, it’s expanding with multicore support, AI integration, and improved documentation. At Embedded World 2025, Zephyr was highlighted as a leading open-source RTOS for future-proof embedded systems.
Industry Adoption
- FreeRTOS:
- Supported by STMicroelectronics STM32, Espressif ESP32/ESP8266, Microchip AVR & SAM devices.
- Integrated into AWS IoT services.
- In May 2025, STMicroelectronics confirmed FreeRTOS as the main kernel for STM32 ecosystems with enhanced middleware.
- Zephyr:
- Adopted by Nordic Semiconductor (nRF Connect SDK), Intel, NXP, STMicroelectronics, Texas Instruments, and Ambiq.
- June 2025: Renesas and Wind River became platinum members; Blecon and Embeint joined as silver members.
- IAR added full production-ready support starting July 2025.
Learning Path & Tutorials
FreeRTOS
- FreeRTOS Documentation
- Mastering the FreeRTOS Real Time Kernel (PDF)
- FreeRTOS GitHub
- FreeRTOS Tutorials on YouTube
- Official FreeRTOS Blog
- NamasteDev Blog – FreeRTOS Hands-On
- Medium – Mastering FreeRTOS
- Percepio Blog – Debugging FreeRTOS
- FreeRTOS Forums Tutorials
Zephyr
- Zephyr Documentation
- Zephyr GitHub Repository
- Nordic Academy – Zephyr Courses
- Witekio Zephyr Guide
- Memfault – Practical Zephyr Blog Series
- DigiKey Zephyr Tutorial Series
- Golioth Blog – Free Zephyr Training
- Synopsys Blog – Zephyr in Silicon Lifecycle Management
- Zephyr Project Blog
- Nordic Webinar (July 2025): Zephyr for Secure IoT
Recommended Books
FreeRTOS
- Mastering the FreeRTOS Real Time Kernel – Richard Barry
- Real-Time Embedded Multithreading Using FreeRTOS – Edward L. Lamie
- Hands-On RTOS with Microcontrollers – Brian Amos
Zephyr
- No major dedicated books (as of 2025), but rely on:
- Official Zephyr Project Documentation
- Vendor SDK guides (Nordic nRF Connect SDK, NXP MCUXpresso)
- Blogs, tutorials, and Linaro Zephyr training
Conclusion
If you need simplicity and minimal resource use, FreeRTOS is still unbeatable. If your project demands connectivity, security, and scalability across multiple platforms, Zephyr is the better long-term investment. With Zephyr 4.1 and FreeRTOS V11.2.0 both released in 2025, the competition is heating up, and both ecosystems are evolving rapidly to meet the next generation of IoT and embedded systems.
