Anyone remember Tom's Rescue Disk? This linux-on-a-floppy was a must-have for rescue and recover back in the day... The web site lives on, but many of the links are 404'd
QNX was ahead of its time. I think it underpinned most versions of the BlackBerry OS and is used in cars / infotainment systems, but I think they would have made a killing in the IoT space if they had developed in another era.
QNX was only used in BB10, which was only introduced after the fall of BlackBerry's popularity (and, arguably, was part of the reason for their old products stagnating)
From that era, I also remember muLinux, which packed quite a lot onto some superformatted floppies.
This comment made me smile - growing up in west Africa this was my first Linux - its modular nature let me download a floppy disk's worth of sub system every week, using the 1 to 2 hours of Internet access that I got for the week, slowly building up from scripting languages all the way up to X11.
Fun times :)