RT-Thread is an open-source real-time operating system (RTOS) for embedded systems and Internet of things (IoT).

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.

As of August 2020[update], RT-Thread was reported to be #3 on the list of RTOSes with the largest number of contributors (behind Zephyr and Mbed).

[3] In 2006, RT-Thread began as an open-source real-time operating system (RTOS) 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 (ROM) and 1.2 kB random-access memory (RAM).

Also, RT-Thread's first variant was named Standard, and second variant was named Nano.