ChibiOS/RT

ChibiOS/RT is a compact, fast real-time operating system for microcontrollers that Giovanni Di Sirio first released in 2007, supporting multiple processor architectures. Its kernel is tiny, ranging from about 1.2 to 5.5 kibibytes depending on which subsystems are enabled, and it can create more than 220,000 threads a second while switching context in roughly 1.2 microseconds on a 72 megahertz STM32 chip. It supports preemptive multithreading across 128 priority levels along with mutexes and semaphores for synchronization, and its hardware abstraction layer covers many ARM Cortex variants as well as PowerPC and AVR processors. It is distributed under a mix of the GNU General Public License version 3 and the Apache License 2.0, with commercial licenses also available, and it ships alongside companion projects such as ChibiOS/HAL and the Eclipse based ChibiStudio development environment. This description is adapted from Wikipedia contributors under CC BY-SA 4.0; changes were made. https://creativecommons.org/licenses/by-sa/4.0/