#QNX is free for non-commercial use again: https://www.qnx.com/products/everywhere/
They even published a RPi image.
Though HN comments remind that it happened at least twice, and make stakes on how long will this version persist: https://news.ycombinator.com/item?id=42079460
But anyway that's a great opportunity to have a hands-on on the de-facto industry standard RTOS
@rayslava have you figured out, where could use it?