RT-Thread

RT-Thread is an open-source real-time [operating system] for embedded systems and Internet of things. It is developed by the RT-Thread Development Team based in China. RT-Thread is aimed to change the current situation in China that there is no well used open-source real-time operating system in the microcontroller field.
, RT-Thread was reported to be #3 on the list of RTOSes with the largest number of contributors.

Variants

In 2006, RT-Thread began as an open-source real-time operating system that is mainly written in the programming language C. In 2017, a second variant was released for resource-constrained microcontrollers; it needs a minimum of 3 kB flash memory or read-only memory and 1.2 kB random-access memory. Also, RT-Thread's first variant was named Standard, and second variant was named Nano.