README.md: add Related Projects

advertize Ariel OS

README.md

@@ -82,6 +82,15 @@ RIOT provides features including, but not limited to:
 * UWB
 * Bluetooth (BLE) via [NimBLE](https://github.com/apache/mynewt-nimble)
 
+### Related Projects
+
+- [**Ariel OS**](https://github.com/ariel-os/ariel-os) is an offspring of RIOT written
+in Rust following RIOT's goals and [vision](https://doc.riot-os.org/vision.html).
+- [Contiki(-NG)](https://github.com/contiki-ng/contiki-ng) was an inspiration for starting RIOT, an operating system for constrained devices with a focus on networking.
+- [NuttX](https://github.com/apache/nuttx) is another general purpose microcontroller OS with a focus on bringing POSIX to MCUs
+- [RT-Thread](https://github.com/RT-Thread/rt-thread) is a microcontroller operating system with strong roots in China and a large community there, it has extensive support for MCUs from Chinese vendors, but also for western ones.
+- [Zephyr](https://github.com/zephyrproject-rtos/zephyr) is a general-purpose operating system for microcontrollers, shepherded by the Linux foundation.
+
 ## Getting RIOT
 
 The most convenient way to get RIOT is to clone it via Git