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Free, extremely simple, amazingly tiny and very fast real-time operating system (RTOS) designed for deeply embedded applications. Target: ARM Cortex-M, STM8. It was inspired by the concept of a state machine. Procedure executed by the task (task state) doesn't have to be noreturn-type. It will be executed into an infinite loop. There's a dedicated function for immediate change the task state.


  • kernel can operate in preemptive or cooperative mode
  • kernel can operate with 16, 32 or 64-bit timer counter
  • kernel can operate in tick-less mode
  • spin locks
  • signals (clear, protect)
  • events
  • flags (any, all, protect, ignore)
  • barriers
  • semaphores (binary, limited, counting)
  • mutexes (recursive, priority inheritance, robust)
  • fast mutexes (error checking)
  • condition variables
  • memory pools
  • stream buffers
  • message buffers
  • mailbox queues
  • job queues
  • event queues
  • timers (one-shot, periodic)
  • cmsis-rtos api
  • cmsis-rtos2 api
  • nasa-osal support
  • c++ wrapper
  • all documentation is contained within the source files
  • examples and templates are in separate repositories on GitHub
  • archival releases on sourceforge


ARM CM0(+), CM3, CM4(F), CM7


This project is licensed under the terms of the MIT License (MIT).