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Femto OS

Free

a very concise portable real time - preemptive operating system (RTOS) for embedded microcontrollers with minimal ram and flash, say 2KB .. 16KB flash and 128 .. 1024 bytes ram.

FreeFree tier
Type
Open Source
Visit Website GitHub (40 stars)

About Femto OS

Femto OS is a very concise, portable, real-time preemptive operating system (RTOS) designed for embedded microcontrollers with extremely limited resources—typically 2 KB to 16 KB of flash and 128 to 1024 bytes of RAM. It supports shared stacks to reduce memory usage (e.g., running 8 tasks and the OS in only 47 bytes of RAM), boasts over 44 ports, and includes a GCC-based toolchain with an installer for AVR Studio. The OS has been used in home automation projects (TempleTronics) and low-power LoRa/Sigfox applications. Development slowed after 2015, but the source code remains available on the website.

Key Features

Extremely small footprint (tasks and OS can run in as little as 47 bytes of RAM)
Preemptive real-time multitasking
Shared stack mechanism to reduce RAM usage when tasks don't run concurrently
Portable across many microcontrollers (44+ ports)
GCC-based toolchain with AVR Studio installer
Suitable for low-power applications (LoRa/Sigfox)
Open source under a free license

Pros & Cons

Pros
  • Ultra-low memory usage allows running on very small microcontrollers
  • Preemptive scheduling for responsive real-time tasks
  • Shared stacks save significant RAM when tasks are mutually exclusive
  • Wide range of supported microcontroller ports
  • Free and open source with no licensing fees
Cons
  • Development has been inactive since 2015 (last news update)
  • Experimental features (like shared stacks) may have unexpected bugs
  • Documentation and support are limited to a forum (no active community)
  • Not suitable for more complex applications requiring extensive OS services

Best For

Home automation (e.g., TempleTronics project)Low-power IoT devices using LoRa/SigfoxEmbedded systems with severe RAM/Flash constraintsEducational projects for learning RTOS concepts

FAQ

What is Femto OS?
Femto OS is a very concise, portable, real-time preemptive operating system (RTOS) for embedded microcontrollers with minimal RAM and flash—typically 2 KB to 16 KB flash and 128 to 1024 bytes RAM.
Is Femto OS still actively developed?
The last news update is from August 2015, indicating new plans and a move to GitHub, but no further releases have been announced since then. Development appears inactive.
How can I get support for Femto OS?
Support is provided via the forum on the Femto OS website. The developer requests that users do not email support questions directly, as his time is limited.
What microcontrollers does Femto OS support?
Femto OS has over 44 ports, including AVR microcontrollers. The website provides a list of supported devices in the 'Ports' section.
Is Femto OS free to use?
Yes, Femto OS is open source and free to use. The source code is available on the website, and there is no licensing fee.