Free real-time operating system (RTOS) designed for deeply embedded applications
C C++ Objective-C


Free, extremely simple, amazingly tiny and very fast real-time operating system (RTOS) designed for deeply embedded applications. Target: ARM Cortex-M family. 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 works in preemptive or cooperative mode
  • kernel can operate in tick-less mode (32-bit timer required)
  • signals (clear, protect)
  • events
  • flags (any, all, protect, ignore)
  • barriers
  • semaphores (binary, limited, counting)
  • mutexes (recursive and priority inheritance)
  • fast mutexes (non-recursive and non-priority-inheritance)
  • condition variables
  • memory pools
  • message queues
  • mailbox 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 GNU GENERAL PUBLIC LICENSE Version 3.