Lightweight, Portable RTOS Scheduler
C C++ Assembly Makefile Other
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Atomthreads is a free RTOS for embedded systems, released under the flexible, open source BSD license and is free to use for commercial or educational purposes without restriction.

It is targeted at systems that need only a lightweight scheduler and the usual RTOS primitives. No file system, IP stack or device drivers are included, but developers can bolt on their own as required. Atomthreads will always be a small number of C files which are easy to port to any platforms that require threading by adding a simple architecture-specific file.


All documentation is contained within the source files, commented using Doxygen markup. Pre-generated documentation can be accessed at

See also the README file contained within each folder of the source tree.


Building of the sources is carried out from the ports tree. For example to make a software build for the AVR architecture see ports/avr/README.


  • kernel: Core kernel sources
  • tests: Automated test suite
  • ports: CPU architecture ports


  • Continuous Integration hosted at Build Status