Crazy as it sounds BeOS wouldn't run on X86 for the first few years. They were trying to capture away Apple people. Also it was close to being the OS X successor, but Apple walked away when BeOS upped the price.
PS The only desktop OS that could pull off this stunt. Play a bunch of videos and music files and unplug the computer. Boot back up and everything is playing again just as you left it.
NeXTSTEP was Steve Jobs' attempt to build an OS that fulfilled the promise of what he saw during his visit to PARC (as opposed to just the graphical interface which is what was implemented with the Mac). It was a true-multi-user Unix with a beautiful UI and an object-oriented framework that was far more influential than its marketshare would have suggested (it led to Microsoft starting Cairo, IBM building WorkplaceOS, and Apple/IBM sinking fortunes and thousands of man-hours into Taligent/Pink).
BeOS was Jean-Louis Gasse's attempt to build a successor to the Mac (including Quicktime which came after Jobs) but built to be multiprocessor and SMT (symmetric multitasking) friendly from the start. It was --like the Mac-- a single-user OS but intended to extract all the performance possible from "modern hardware"
ACCESS Co. the current owner of the PalmOS and BeOS assets basically frittered away whatever potential BeOS had. So it definitely flopped.