I ran BeOS as a daily driver for a few months in the early 2000s. I had a winmodem and Linux couldn't connect to the internet for me, but for some reason, BeOS had drivers, so I used it. It was faster and the desktop environment felt more polished than KDE/Gnome.
Of course, at that time, it was impossible to know which OS would win the wars, so BeOS became my favorite. However, Linux developed very quickly during those years, I got into college and started using UNIX there, winmodem drivers appeared, and that's what I ended up using.
But BeOS still holds a very dear place in my heart. It really was superior to anything else during that era.
+1. Even though it had limitations, it had this "clean polished feeling"
What set it apart was the out of the way UX and clean fast experience. It was a real time kernal to boot. I think korg used it on some of their synth products or something even.
To me the UX and experience on it was (still) ahead of its time. It ran stuff on a Pentium 90 like it was a 400mhz beast running NT.