1. \FreeRTOS\FreeRTOS_v202012.00\
FreeRTOS is freely available under a MIT license.The source code is derived from "https://freertos.org/".

2. \RTOS\RT-thread\Pack\RealThread.RT-Thread.3.1.5.pack
RT-Thread 3.0 is freely available under a Apache License 2.0.The source code is derived from "https://www.rt-thread.org/download/mdk/".

3. \RTX5\
Keil RTX5 is an open-source, deterministic real-time operating system implementing the CMSIS-RTOS v2 API, a generic RTOS interface for Cortex-M processor-based devices.The website is"https://www2.keil.com/mdk5/cmsis/rtx"